Central AC with too much air?

[smoss]

You guys have been great answering everyone's questions (along with a few of mine). I have a duct type question I would like to get some opionions on. I am in a condo, unit above me, below me, and behind me. I face west, lots of windows in Vermont. The units on West side of buiding have 2 tons of cooling (1200 sqft). Pretty sure it is oversized from what I read on here. For example when it does reach 90 here, unit never runs more than 15 minutes. Also, I really feel the air a lot. I can never seem to get a good setting on the tstat. Sometimes feels to hot or too cold. I got a good vision pro 8000 and that helped a lot but still, I can surely feel and hear it when it's on.

Anyway, I have one metal duct that runs through the center of the apartment. It is roughly 28" by 7 " in an enclosed soffit (8 foot ceiling in the apartment). The duct is roughly 20 feet long and all registers come off that one main duct. I have 6 registers.

2 7" by 6"
2 9" by 6"
1 6" by 18"
1 13" by 18"

All are rough measurements of the outside of the grill. In all cases the actual opening is slightly smaller. My fan coil is mounted in a small closet not ducted return. The fan coil on a pedestal and there is simply a return grill in the side of the closet. The return grill is 17" by 9". Also, the door to the closet has a 1 inch opening around the entire parameter so it also functions as a return. Roughly another 150 sq inches by my calcs. So after reading on here looks like my return is undersized. Problem is if I open the door to the closet, essentially making my return size 1026 sq inches.. HUGE. I didn't see any difference in the supply air from the registers. So that led me to believe I am starved on the supply side. So I decided to take the grills off and I found a removable back piece that allows you to shut the vent. I took all of these off. See pic.

I then had tons of air so I thought I did a good thing. I then saw a difference when opening and closing the HVAC closet door. Problem now is I was getting too much air!! You can now see the leaves on the plants on the other side of the room blow quite a lot. Also, I got lots of duct noise. Like the duct metal was flexing. Also, as you guys realize, my humidity level increased a little bit. It was around 55% when it was in the 60's outside and raining.

So I then went into the air handler and set the CFM adjust to low. As I am sure you know, that allows the air to be reduced by roughly 10% from nominal. I still had a lot of air coming out of the vents, but it was a little better. Still had duct noises.

So, now I have put the metal pieces back on the grills. I call them restricters. My own termonology since they do seem to restrict the air. The fan coil is still on low setting. Now the AC is much quieter, no more duct noises and I feel the coolness without feeling the breeze if you know what I mean. It feels as it should. I have lived in houses that have central air and I know shouldn't feel the AC so much as I did. It nows feels better than it ever has. The temp seems more consistent too.

I know you guys are going to tell me they should have done a calc and the ducts should be done correctly. This condo is 2 years old so none of that is going to happen. The ducts are buried in sheet rock soffits so they aren't changing.

My question is IF, and I do mean IF, I never get a freeze up of the coil, am I ok with the way things are? I will check the coil for the next few days and see if I get low air flow. If there is ice, I will go back to nominal and leaves things alone. If I don't get ice, then is there a problem running partially starved of air? I am thinking maybe early motor failure? I think just the motor can be changed so if that goes out in 5-6 years I think it's worth it for the quiet and confort.


Any thoughts? Am I crazy?

Here are some pics to help you guys.

[Shophound]

Where you might get in trouble is with your compressor. An iced up coil involves more than just a bunch of ice crystals blocking air flow and eventually stopping the system from cooling. It can also take out a compressor, due to liquid refrigerant flooding back to the compressor.

I never change blower speeds on an a/c without checking the refrigerant charge afterward.

[smoss]

A few weeks ago I had a low ambient kit installed (fan cycler and crankcase heater). It will cycle off the condenser if pressure builds to high. I know this is meant for low ambient temperatures, but would it possibly help stop liquid from ending back up at the condenser? Maybe I am totally off.

Will I know if liquid ends up back at the condenser? Wouldn't I need to see ice before that happens?


Thanks for reading my long long post.

[ldmth44]

A low ambient kit will cycle condenser fan on or off or modulate condenser fan speed to maintain an adequate head pressure in the system for optimal operation, if adjusted properly. You don't necessarily need to see ice to have liquid refrigerant back to the compressor. Sounds like you need a tech to analyze your system and correct the issues your having. Could be airflow, mischarged system or other causes that need to be addressed.

[smoss]

A low ambient kit will cycle condenser fan on or off or modulate condenser fan speed to maintain an adequate head pressure in the system for optimal operation, if adjusted properly. You don't necessarily need to see ice to have liquid refrigerant back to the compressor. Sounds like you need a tech to analyze your system and correct the issues your having. Could be airflow, mischarged system or other causes that need to be addressed.

With the fan speed on nominal it works fine. No problems as long as the grill backs are on like they are now. So now everything is like when I bought the place. I just like the lower fan speed for comfort and noise. Maybe I should put it back to normal and live with the slightly higher noise level.

FYI info, it has just been running for around 10 minutes. Inside temp set at 73 degrees, outside temp is 68 degrees. Kinda humid out that is why the AC is on.

The small copper pipe is still very warm. So I think I don't have liquid going to the condenser as long as that pipe stays warm, not cold. I can easily check that pipe for the next few days since all I have to do it open the closet door.

I'd hate to call a tech because it is working fine. I just like the lower fan speed.

[ldmth44]

One can't assume a system is running fine just by the sensed temperature of the liquid or suction line. There are too many variables to consider to be sure that a system is running properly. If there are any doubts, you should have system checked by a pro.

I would personally feel better if my auto mechanic checked my emmissions system on my car other than relying on "feel" that my engine is fine and making adjustments myself, since I know a bit about an engine but not all that is required to make it run right continuously without proper training.

[smoss]

One can't assume a system is running fine just by the sensed temperature of the liquid or suction line. There are too many variables to consider to be sure that a system is running properly. If there are any doubts, you should have system checked by a pro.

I would personally feel better if my auto mechanic checked my emmissions system on my car other than relying on "feel" that my engine is fine and making adjustments myself, since I know a bit about an engine but not all that is required to make it run right continuously without proper training.

Ok. Thanks. I guess I am kinda confused because there are two jumpers on that fan coil. One, lists the compressor size that the coil is connected to. For example, mine is clearly on 024 which is the model of compressor I have. The HP/AC adjust, can be adjusted for low, nominal or high which is -10%, nominal, or +15% to allow for comfort settings (ie noise and humidity removal). It says this right in the install manual.

So I took that as being I can move the low, nominal, or high as long as I don't touch the more important compressor choice jumper.

I am actually on the association for my building and I was instrumental in getting a contract for our HVAC company to inspect all our fan coils twice a year and compressors once a year. So I do understand the importance of getting a pro to look at it, I just didn't think this minor change was am issue.

I switched it back to nom, where it was, and I will call them tomorrow. They know our systems very well since they are always here. Hopefully they can let me know over the phone. In my experience they don't like to come out unless something is broken. They are very busy all the time.

[ldmth44]

Peace of mind knowing it is done right is better than trying something yourself and screwing it up. Even I had to learn that the hard way, we all eventually do. Good luck!

[ticotech cayman]

the manual will tell the min cfm for ur ahu, but u deffinily have to check the system 's pressures. the compressor could be flooding with liquid freon and not necesary icing up at the evap.

[smoss]

the manual will tell the min cfm for ur ahu, but u deffinily have to check the system 's pressures. the compressor could be flooding with liquid freon and not necesary icing up at the evap.

You guys are making this much too dificult on me. I simply wanted to lower the fan speed. :D Just kidding.

I have to say I always thought HVAC was rather simple until reading this forum. Also, this is residential type stuff. I was out in Vegas a few weeks ago and saw the HUGE cooling towers behind every hotel to keep all that sq footage cool. It is quite impressive. I can't even imagine all the issues with keeping those systems running in 120 temps.

Thanks for all your help. I might just leave my unit on high and live with the slightly increased noise and air. If I am still in my apartment when the HVAC needs to be replaced, I am going for a 1.5 Ton unit.

[motoguy128]

Also, this is residential type stuff. I was out in Vegas a few weeks ago and saw the HUGE cooling towers behind every hotel to keep all that sq footage cool. It is quite impressive. I can't even imagine all the issues with keeping those systems running in 120 temps.
.


Actually, the cooling towers work very well in the hot dry desert air. Cooling towers require regular maintenance to keep them clean nad the proper chemical levels. The cooling towers however, are just 1/2 of the system. What you didn't see are the numerous chillers located inside the building... located in large mechanical rooms along with the boilers and numerous pumps. The chillers are basically really big A/C compressors, that use water instead of air to cool the condenser coil. The heat is removed by sing evaporation in the cooling tower to cool the water.

They are pretty cool. At my work, in 1 building we have 5 chillers, 2 big onces and 3 smaller ones that are staged depending on the heat load in the process. It seems like at least 1 or 2 are always down for maintenance or tripped out on some safety or another. Probably installed incorrectly by our engineering group.

[Shophound]

A few weeks ago I had a low ambient kit installed (fan cycler and crankcase heater). It will cycle off the condenser if pressure builds to high. I know this is meant for low ambient temperatures, but would it possibly help stop liquid from ending back up at the condenser? Maybe I am totally off.

Will I know if liquid ends up back at the condenser? Wouldn't I need to see ice before that happens?



A low ambient kit is for when outdoor temperatures are below the normal operating envelope of an a/c condenser. It works by keeping head pressure high enough so the right amount of refrigerant will flow through the evaporator, allowing interior cooling to continue normally. Low ambient kits are typically found in commercial HVAC systems that must operate for most or all of the year, such as office buildings with air cooled equipment, or computer rooms.

It is still possible to freeze an indoor coil that has a low ambient kit installed on the outdoor unit. I've seen it happen on variable speed air handlers used in VAV applications where the hot gas bypass was not adjusted correctly. For a residence, if everything about the system is normal and the coil is freezing, there simply is not enough heat load in the house to keep the coil surface temperature above freezing. Running the a/c to dehumidify a house during cool, damp weather can put a coil at risk for freezing over.

Being you live in a condo, you could have moisture entering your unit from untold sources, plus the moisture you create by showering, laundry, cooking, etc. Have you ever measured what the humidity runs at in your unit on a day to day basis? Do you base your need to dehumidify (when it is cool outside) because the air in the condo feels "stuffy"?

[smoss]

Actually, the cooling towers work very well in the hot dry desert air. Cooling towers require regular maintenance to keep them clean nad the proper chemical levels. The cooling towers however, are just 1/2 of the system. What you didn't see are the numerous chillers located inside the building... located in large mechanical rooms along with the boilers and numerous pumps. The chillers are basically really big A/C compressors, that use water instead of air to cool the condenser coil. The heat is removed by sing evaporation in the cooling tower to cool the water.

They are pretty cool. At my work, in 1 building we have 5 chillers, 2 big onces and 3 smaller ones that are staged depending on the heat load in the process. It seems like at least 1 or 2 are always down for maintenance or tripped out on some safety or another. Probably installed incorrectly by our engineering group.


Actually, where I work we have several test floors. On the test floors are large testers that have 200 amps service each. There might be 5-10 of these in one room. So as you can imagine, we have big chillers on the floor to keep things cool. When a chiller fails, the test floor rises to 90 degrees within 30 minutes. Also, the chillers natrually run all winter long (even in Vermont in winter). I heard recently we are using outside air to cool instead of the cooling towers when ambient air is below 30 degrees. Sounds like a good idea sine almost all winter it is very cold.

[smoss]

A low ambient kit is for when outdoor temperatures are below the normal operating envelope of an a/c condenser. It works by keeping head pressure high enough so the right amount of refrigerant will flow through the evaporator, allowing interior cooling to continue normally. Low ambient kits are typically found in commercial HVAC systems that must operate for most or all of the year, such as office buildings with air cooled equipment, or computer rooms.

It is still possible to freeze an indoor coil that has a low ambient kit installed on the outdoor unit. I've seen it happen on variable speed air handlers used in VAV applications where the hot gas bypass was not adjusted correctly. For a residence, if everything about the system is normal and the coil is freezing, there simply is not enough heat load in the house to keep the coil surface temperature above freezing. Running the a/c to dehumidify a house during cool, damp weather can put a coil at risk for freezing over.

Being you live in a condo, you could have moisture entering your unit from untold sources, plus the moisture you create by showering, laundry, cooking, etc. Have you ever measured what the humidity runs at in your unit on a day to day basis? Do you base your need to dehumidify (when it is cool outside) because the air in the condo feels "stuffy"?


Actually, good thing you bring this up. Being in a condo I have a large heat load all the time. For example, when I am at my parents house in NY, they might leave their thermostat on 72 over night. Outside temp gets into the 50's. The next morning the Tstat will say 69 degrees and AC not running of course. My condo, if outside temp drops into 50's, and tstat set at 72. It will still be running in the morning and maintaining 72. My place is insulated very well and I have units around mine (above, behind below etc). So that is one reason I went with the low ambient kit. In Vermont it we have regular summer lows in the low 60's and high 50's. For example last night it was in the 50's.

I am very sensitive to humidty. I always have been. I sweat like crazy when humidity is high even if ourside temp is in the 60's. I have always been like that compared to other people. My place was around 46% last week when the outside temp was in the 70's and dry. Lately it has been raining lots and outside humidty is in the 80's or 90's. My place is around 52% even with showers and inside temp set at 72 or 73 and AC running.

I do have a bathroom exhaust fan that runs 24/7 in order to provide fresh air. This is per code for new construction. I can adjust it's speed. I have it on medium. I always thought, expecially after reading on here, that the speed should automatically adjust depending on outside and inside humidity and temp levels. It doesn't. That would be asking too much. They simply turn the fan on, leave it on, to meet code. I have to take the faceplate off to adjust speed since you aren't supposed to touch it. There is no way to shut it off unless you take the faceplate off. On top of this issue, my condo is in a building and opens to an enclosed hallway. I assume more air is taken from the hallway as compared to outside. The returns in for the HVAC in the hallway, is one tiny little 8 inch square per floor. I assume they are relying on air being drawn into the condos to keep down odors and humidity as well.

Hope that provides a better picture of the place. I am no expert here, but I think in my situation, I am fairly unlikely to freeze my indoor coil even on low speed given the fact I have such a high heat load in my place at all times. I have put it back to nominal mode though. It was louder and more air with that setting. Maybe it's picky, but I hate feeling the AC so much. It's better to not notice when it cycles. The AC guys think you are crazy if you complain about problems like this. As long as it's cold, there is nothing wrong. It reminds me a lot of going to the car dealership and complaining about a rattle. They look at you like you are crazy or something.... :p

[motoguy128]

I think you underline a good point... that the HVAC pros are always trying ot make on here. You heat load is not dependant on the size of the home. Acutally, the heat load will be comparatively higher on a small home than a large home.

Why? Because the surface areas to volume ratio is greater. This is the same reason a 16oz plastic bottle of soda has a shorter shelf life than a 2 liter bottle.

Second, many heat loads are not dependant on the size of the home... rather the number of occupants, and some are more constant. Whether you have 1 or 4 occupants, you normally only have 1 TV on. 4 occupants will take more showers. And more occupants will require more heat for cooking a larger amount of food. There's also the body heat. 1 human can produce around 5000 BTU's per day.

So in a small space, if nothing else, you may need quote a bit of latent capacity to remove humidity.

The more informaiton I read and more I think about the issue, it seems that many homes really would benefit more from a whole house dehumidifer. With RH down to 45%, 75F can feel MORE comfortable than 72F and 60%RH.... which is where many home end up. But on a 68F day, you will need very little sensible capacity to maintain 75F indoors unless you hav a lot of direct sun.

[Shophound]

Smoss,

In all honesty, I think your constantly running bath fan is contributing considerably to your humidity problem. I've seen this situation in hotels, where the hallway is pressurized via either an induction fan or a dedicated outdoor air system (DOAS) that cools and dehumidifies outdoor air prior to injecting it into the hallway. The idea is by pressurizing and conditioning the hallway air, it is the conduit whereby the individual rooms/units can be ventilated.

When a hallway is pressurized like this, it pressurizes everything connected to it. So while there may be make-up air provisions for each unit's bath ventilators, any door adjoining the hall that is not weatherstripped will also leak air into the unit. As long as the air in the hall is conditioned this might not be a problem, but it could be if the occupant of any given unit prefers an environment different from the hallway. It becomes a big problem if the hallway is merely pressurized with outdoor air that is neither heated or cooled/dehumidified, or the DOAS breaks down.

The constantly running bath fan can also depressurize your unit in respect to not only the hallway, but any other building cavity that can draw air from a non air conditioned area. You could be drawing moisture into your unit from many areas that aren't outright obvious. But...the first question I'd have for the condo board is whether the air in the hallway is treated (heated/cooled/dehumidified) or not. If it's not, as long as you have a constantly running bath fan you'll always be fighting a battle with moisture, given what you've told us about your summer weather.

[smoss]

I think you underline a good point... that the HVAC pros are always trying ot make on here. You heat load is not dependant on the size of the home. Acutally, the heat load will be comparatively higher on a small home than a large home.

Why? Because the surface areas to volume ratio is greater. This is the same reason a 16oz plastic bottle of soda has a shorter shelf life than a 2 liter bottle.

Second, many heat loads are not dependant on the size of the home... rather the number of occupants, and some are more constant. Whether you have 1 or 4 occupants, you normally only have 1 TV on. 4 occupants will take more showers. And more occupants will require more heat for cooking a larger amount of food. There's also the body heat. 1 human can produce around 5000 BTU's per day.

So in a small space, if nothing else, you may need quote a bit of latent capacity to remove humidity.

The more informaiton I read and more I think about the issue, it seems that many homes really would benefit more from a whole house dehumidifer. With RH down to 45%, 75F can feel MORE comfortable than 72F and 60%RH.... which is where many home end up. But on a 68F day, you will need very little sensible capacity to maintain 75F indoors unless you hav a lot of direct sun.


I understand a dehumidifier woudl work the problem I have is that it increases indoor temp which is a problem in my condo that has enough heat. I always joke with my buddy that wants to buy a dehumidifier for his basement but has an extra window AC. I told him to put it on some saw horses with a bucket underneath. :D Any cooling would be balanced by the heat coming off the back since it isn't vented.

For my condo I would like a 2 stage AC that I hear about a lot on here. When I get full sun from the west it is rather strong. No trees to block it since I am 3 floors up.

[smoss]

Smoss,

In all honesty, I think your constantly running bath fan is contributing considerably to your humidity problem. I've seen this situation in hotels, where the hallway is pressurized via either an induction fan or a dedicated outdoor air system (DOAS) that cools and dehumidifies outdoor air prior to injecting it into the hallway. The idea is by pressurizing and conditioning the hallway air, it is the conduit whereby the individual rooms/units can be ventilated.

When a hallway is pressurized like this, it pressurizes everything connected to it. So while there may be make-up air provisions for each unit's bath ventilators, any door adjoining the hall that is not weatherstripped will also leak air into the unit. As long as the air in the hall is conditioned this might not be a problem, but it could be if the occupant of any given unit prefers an environment different from the hallway. It becomes a big problem if the hallway is merely pressurized with outdoor air that is neither heated or cooled/dehumidified, or the DOAS breaks down.

The constantly running bath fan can also depressurize your unit in respect to not only the hallway, but any other building cavity that can draw air from a non air conditioned area. You could be drawing moisture into your unit from many areas that aren't outright obvious. But...the first question I'd have for the condo board is whether the air in the hallway is treated (heated/cooled/dehumidified) or not. If it's not, as long as you have a constantly running bath fan you'll always be fighting a battle with moisture, given what you've told us about your summer weather.

Interesting. I am actually on the association so I know for a fact that there is one comprressor for all 4 floors and the lobby. There are two T stats on teh return air (combined for all 4 floors). One Tstat controls heat and the other controls cool. It only measures return air. As you can imagine, it is hard to keep all 4 floors balanced. Mine hallway is warmer than the 72 I keep my place. I feel the temp difference everytime I enter or leave.

By the way, I can see light from the hallway into my unti through the front door. I am gathering maybe I should seal that door better and play with lowering my bath fan speed.

Do you think 72 and 52% humidity is a lot? I didn't think it was that high.

[Shophound]

I think you underline a good point... that the HVAC pros are always trying ot make on here. You heat load is not dependant on the size of the home. Acutally, the heat load will be comparatively higher on a small home than a large home.

Size of a house is a major component in a heat load calculation. It is not the only factor, but is considerable. The larger a house is, the more surface area is exposed to weather. The configuration of the house also matters. A two story house of 2,000 square feet will have less square footage directly below an attic than a single story house with the same square footage. Yet a two story house, especially as they are built now with higher ceilings, will have an increased issue of stack effect over a single story house. Orientation of the house also figures, as well as the amount and size of glazing on each facade.

Internal sensible and latent gains are noteworthy, but when its broken down for most residential construction, infiltration and glazing are often the biggest contributors to heat gain and loss. A bigger house will likely have larger infiltration and glazing areas than a smaller house, along with increased surface area exposed to weather.



Second, many heat loads are not dependant on the size of the home... rather the number of occupants, and some are more constant. Whether you have 1 or 4 occupants, you normally only have 1 TV on. 4 occupants will take more showers. And more occupants will require more heat for cooking a larger amount of food. There's also the body heat. 1 human can produce around 5000 BTU's per day.


Tighter homes can require more dehumidification due to reduced infiltration, and, as in our OP's case, increased forced ventilation with (possibly) untreated outdoor air. In humid climates, forcefully ventilating a house without first treating the ventilating air is ridiculous.




The more informaiton I read and more I think about the issue, it seems that many homes really would benefit more from a whole house dehumidifer.


For some climates I can see this approach as viable. For my own climate, I have yet to find myself wishing I had one for my house. Vermont may be a humid climate in summer, but it doesn't appear to be a consistently hot one. But...I think the OP has other building ventilation/leakage issues that he may not be aware of, and is causing him to resort to his a/c to seek remedy.

[smoss]

Size of a house is a major component in a heat load calculation. It is not the only factor, but is considerable. The larger a house is, the more surface area is exposed to weather. The configuration of the house also matters. A two story house of 2,000 square feet will have less square footage directly below an attic than a single story house with the same square footage. Yet a two story house, especially as they are built now with higher ceilings, will have an increased issue of stack effect over a single story house. Orientation of the house also figures, as well as the amount and size of glazing on each facade.

Internal sensible and latent gains are noteworthy, but when its broken down for most residential construction, infiltration and glazing are often the biggest contributors to heat gain and loss. A bigger house will likely have larger infiltration and glazing areas than a smaller house, along with increased surface area exposed to weather.



Tighter homes can require more dehumidification due to reduced infiltration, and, as in our OP's case, increased forced ventilation with (possibly) untreated outdoor air. In humid climates, forcefully ventilating a house without first treating the ventilating air is ridiculous.




For some climates I can see this approach as viable. For my own climate, I have yet to find myself wishing I had one for my house. Vermont may be a humid climate in summer, but it doesn't appear to be a consistently hot one. But...I think the OP has other building ventilation/leakage issues that he may not be aware of, and is causing him to resort to his a/c to seek remedy.


The only thing I don't see is the benefit of removing moisture vs. infiltration. If I take a shower, obviously the fan is helping remove the moisture. After an hour, or two hours, or when?? does the fan now start to cause infiltration? I guess as the fan is removing indoor moisture it is also getting air from outside. If that air is drier then it is good. If it is raining, then it's not exactly helping (of course depends on outside temp as well, that dew point thing).

However, this is somewhat off topic from where I started. I just wanted to reduce the fan coil speed for a few reasons. Less air since it blows my plants around on the opposite side of the room, less noise, and more dehumidication. I guess I'll have to call the techs to lower the speed, or just live with the increased air.


By the way, Vermont gets in the low 80's or high 70's on average. Maybe one or two days a summer when it hits 90. Not sure we hit 90 yet, but 3 days were close so far. Night time is almost always in the 60's and sometimes in the 50's. We only have a handful of days when the nighttime low is in the 70's. End of August it starts to get colder.. Night time low's in the 40's by mid sep. I would say. Very short summer. :mad:

[Shophound]

Interesting. I am actually on the association so I know for a fact that there is one comprressor for all 4 floors and the lobby. There are two T stats on teh return air (combined for all 4 floors). One Tstat controls heat and the other controls cool. It only measures return air. As you can imagine, it is hard to keep all 4 floors balanced. Mine hallway is warmer than the 72 I keep my place. I feel the temp difference everytime I enter or leave.

By the way, I can see light from the hallway into my unti through the front door. I am gathering maybe I should seal that door better and play with lowering my bath fan speed.

Do you think 72 and 52% humidity is a lot? I didn't think it was that high.

In terms of total human comfort at normal summertime room temperatures (72-78 degrees), a target for indoor moisture levels is to maintain indoor dew point temperatures below 55 degrees. Why do I mention dew point over relative humidity? Dew point is a more consistent indicator of moisture in the air, for if the amount of moisture in a given sample of air remains the same but the temperature changes, the dew point will not change, whereas the relative humidity will. Over time it has been determined through research that human beings, at normal room temperature ranges, are comfortable in summer when dew point temperatures stay below 55 degrees.

Why mention any of this? Well, I'm arming you with some ways to investigate why you have trouble maintaining a decent environment in your condo. You can play around with the blower speed, and I understand the concurrent noise and air movement concern, but how about going one level higher? Find out why you have this struggle to begin with and then see if there's remedy? Wouldn't it be great if you didn't have to run your a/c when most anyone else would not need to?

Here's a place to start. Get an instrument that can measure temperature and relative humidity with reasonable accuracy. Measure the conditions in your condo and then the hallway. Convert your temperature/humidity combinations to dew point temperatures. This can be done with online calculators so you don't have to mess around with a psychrometric chart. If the dew point out in the hall is consistently higher than 55 degrees, it is likely contributing to your humidity problem. You mentioned the hall being warmer than your condo, so it is also contributing to your heat load. How much warmer would be interesting to know.

By the way, 72 degrees at 52% relative humidity gives you a dew point of ~54 degrees.

[smoss]

In terms of total human comfort at normal summertime room temperatures (72-78 degrees), a target for indoor moisture levels is to maintain indoor dew point temperatures below 55 degrees. Why do I mention dew point over relative humidity? Dew point is a more consistent indicator of moisture in the air, for if the amount of moisture in a given sample of air remains the same but the temperature changes, the dew point will not change, whereas the relative humidity will. Over time it has been determined through research that human beings, at normal room temperature ranges, are comfortable in summer when dew point temperatures stay below 55 degrees.

Why mention any of this? Well, I'm arming you with some ways to investigate why you have trouble maintaining a decent environment in your condo. You can play around with the blower speed, and I understand the concurrent noise and air movement concern, but how about going one level higher? Find out why you have this struggle to begin with and then see if there's remedy? Wouldn't it be great if you didn't have to run your a/c when most anyone else would not need to?

Here's a place to start. Get an instrument that can measure temperature and relative humidity with reasonable accuracy. Measure the conditions in your condo and then the hallway. Convert your temperature/humidity combinations to dew point temperatures. This can be done with online calculators so you don't have to mess around with a psychrometric chart. If the dew point out in the hall is consistently higher than 55 degrees, it is likely contributing to your humidity problem. You mentioned the hall being warmer than your condo, so it is also contributing to your heat load. How much warmer would be interesting to know.

By the way, 72 degrees at 52% relative humidity gives you a dew point of ~54 degrees.

This is very very interesting actually. Other than the air movement and noise I think you are really on to something.

Here is some proof:

I can't truly leave my tstat on one temp. I thought it was the old crappy tstat that would only cycle for 3 minutes, I fixed that. The vision pro is light years better. However, I still can't find a comfortable temp.

For example during the day if it's sunny (dry) and part sun coming in, I can't leave it at 72. I freeze!!! I have to put it on 73 or maybe 74. The AC still runs and everything feels fine. When I got to bed I HAVE to lower it to 72 otherwise like clockwork I will wake up at 4-5 am and be covered in sweat. This is true even with a ceiling fan going above my bed. In the evening I lower it to 72 or on rainy days.

Even on 72, when I wake up I feel warm. The tstat and other thermometers in the entire unit all say around 72 maybe 73 but it feels MUCH warmer. So I think humidity is in fact playing a big part here. People who have visited always comment that a given temp, say 74 feels much warmer at my place than their house. I was a friends house over the weekend and it was 78. It felt ok. A little warm, but still felt cooler than my house at 75 for example.

So you put this all together and humidity must be playing a big role here. I'll try measuring temp and humidity like you suggested. I will also seal up my door and I can try shutting off the fan at least for summer. I think I'll need it again when it gets very very cold in winter. Otherwise I get condensation on the inside of my windows if the fan isn't on high enough. Again, that fan should vary with outiside temp, or use a Air to air exchanger. Not sure how you do that in a condo but I am sure it could be done.

Thanks for all the help so far. I"ll try to do some measurements and post back sometime in the next few weeks.

[Shophound]

What you just said seems to bolster my previous thoughts. During the day when it is sunny outside, the outdoor dew point is lower. In many areas this is a natural daily cycle during the summer. Daily heating dries out the air somewhat. Nighttime cooling increases the outdoor moisture level. If you are constantly drawing in untreated air into your condo, you are at the mercy of these daily swings. At night, your sensible heat load drops off, so your a/c runs less. It can't dehumidify if it can't run. But...that silly bath fan runs non-stop, so it loads your condo with moisture all night long. That is why you wake up in the middle of the night feeling uncomfortable.

You may find the following article interesting, even if it is a little on the technical side:

http://www.buildingscience.com/documents/digests/bsd-109-pressures-in-buildings?full_view=1

Toward the middle it deals with building configurations similar to your condo, particularly where it discusses hotel air pressurization. Check it out.

[smoss]

What you just said seems to bolster my previous thoughts. During the day when it is sunny outside, the outdoor dew point is lower. In many areas this is a natural daily cycle during the summer. Daily heating dries out the air somewhat. Nighttime cooling increases the outdoor moisture level. If you are constantly drawing in untreated air into your condo, you are at the mercy of these daily swings. At night, your sensible heat load drops off, so your a/c runs less. It can't dehumidify if it can't run. But...that silly bath fan runs non-stop, so it loads your condo with moisture all night long. That is why you wake up in the middle of the night feeling uncomfortable.

You may find the following article interesting, even if it is a little on the technical side:

http://www.buildingscience.com/documents/digests/bsd-109-pressures-in-buildings?full_view=1

Toward the middle it deals with building configurations similar to your condo, particularly where it discusses hotel air pressurization. Check it out.


Thanks. I'll read this tonight when I have more time. I don't mind the technical stuff. I do find this stuff interesting. I think the humidity sounds like it explains some of my problems. I always wondered why this condo seems to change in feel all the time. I have lived in places with central air and didn't have to adjust the Tstat much at all.

[smoss]

What you just said seems to bolster my previous thoughts. During the day when it is sunny outside, the outdoor dew point is lower. In many areas this is a natural daily cycle during the summer. Daily heating dries out the air somewhat. Nighttime cooling increases the outdoor moisture level. If you are constantly drawing in untreated air into your condo, you are at the mercy of these daily swings. At night, your sensible heat load drops off, so your a/c runs less. It can't dehumidify if it can't run. But...that silly bath fan runs non-stop, so it loads your condo with moisture all night long. That is why you wake up in the middle of the night feeling uncomfortable.

You may find the following article interesting, even if it is a little on the technical side:

http://www.buildingscience.com/documents/digests/bsd-109-pressures-in-buildings?full_view=1

Toward the middle it deals with building configurations similar to your condo, particularly where it discusses hotel air pressurization. Check it out.


Very interesting. This setup looks a lot like my place. Except, I don't have metal studs, and my fan coil is in a closet not in the ceiling. I would love to know what I can do to lower my humidty level.

I got home last night, Tstat set at 76, humidty was 55% in my place I shut off ventilator fan, lowered temp to 72. I also changed tstat to run auto, not circ mode.
When I went to bed, 72 and 51% humidity inside, 64 and lots of humidity outside. We got a bad storm yesterday evening. Lots of rain.

This morning, 72 in house, 53% humidity. It was only overnight but humidity got in, or it was the dishwasher I ran last night. I took a shower, turned on fan, humdiity was 54% inside and 72 degrees when I left.

Other than installing a dehumidifier I don't see how to lower the humdity. Maybe insulating my front door and sealing up the fan coil closet better? I like the idea of being more comfortable with less energy. I think Americans tend to waste much too much energy in general. cars. hot water heaters as oppposed to on demand.. etc.. the list goes on. Any other thoughts?

I think lower the fan coil speed would only help remove more moisture so why not.

Another crazy idea I had was to install a electric heater stip in my fan coil. I know this blows away my idea of conserving energy but I am sure it would act as a dehumidifer. Isnt' it essentially the same thing? Cool the air then heat it up a bit. I am sure we could come up with a control to turn on the
electric stip when a call for dehumidification was sent. Nobody in this state uses a heat strip since our electric rates are close to 20cents per kilowat hour.

[Shophound]

What would be helpful is what your morning wake-up conditions were prior to you turning the bath fan off and leaving the blower in "auto" mode (where it ALWAYS should be in humid climates, NEVER use "circ" or "on").

You are battling two issues...air intruding your condo from sources exterior to your unit, and reduced run times of the a/c at night due to reduced sensible heat gain to the structure. If in the end you find you can't do much about the moisture and air instrusion into your unit, you are a prime candidate for our resident dehumidifier person Teddy Bear to discuss whole house dehumidification. These units have the reheat feature you speak of (and don't need electric heat strips to get it done), and do it better than using a/c for dehumidifying under the conditions you talk about for your condo.

Are you listening, Teddy? I just gave you a good plug. :D

[motoguy128]

What you just said seems to bolster my previous thoughts. During the day when it is sunny outside, the outdoor dew point is lower. In many areas this is a natural daily cycle during the summer. Daily heating dries out the air somewhat. Nighttime cooling increases the outdoor moisture level. If you are constantly drawing in untreated air into your condo, you are at the mercy of these daily swings.


That's interesting because it tends to be oposite of my observations...at least here in the midwest. In a static weather system... during the daytime, the radiant heat from the sun, evaporates moisture and raises the dewpoint. This is combined with evaporation from plants trying to move water up to the leaves and cool themselves. The RH of course drops, because temprature increases.

At night time, if the dewpoint approaches the dry bulb temp, which is common, you get condensation which then drops the dewpoint to a tmeprature near the dry bulb temp. So overnight temps have a limiting effect on dew point. Although most moiture is dependant on the climate and weather system. ir comming from the north is cooler and dryer, air form the south is hot and humid from the Gulf of Mexico. When they meet, you get thunderstorms. A stagnant system comming form the west over the mountians can be hot and dry.


The phenomonom you point out, may be related to air movement near bodies of water where cooler, but very humid moves off the water during the night and during the day hot dryer air comes from the land.


Please correct me if I have anything wrong.

[smoss]

What would be helpful is what your morning wake-up conditions were prior to you turning the bath fan off and leaving the blower in "auto" mode (where it ALWAYS should be in humid climates, NEVER use "circ" or "on").

You are battling two issues...air intruding your condo from sources exterior to your unit, and reduced run times of the a/c at night due to reduced sensible heat gain to the structure. If in the end you find you can't do much about the moisture and air instrusion into your unit, you are a prime candidate for our resident dehumidifier person Teddy Bear to discuss whole house dehumidification. These units have the reheat feature you speak of (and don't need electric heat strips to get it done), and do it better than using a/c for dehumidifying under the conditions you talk about for your condo.

Are you listening, Teddy? I just gave you a good plug. :D

Actually, the day before had very very similar conditions. When I woke up humidity was same, 53% and temp of 72. I didn't see much of a chance with the fan being set to auto and the fan off. Also note that I had the circ feature only programmed during the day, not at night. I did that to help reduce humidity at night when the ac runs less. I now have it set to auto 24/7. I am hoping I might see the humidity drop after a few days vs. just overnight. I know it takes a while to for humidity to change.

I am still confused about ifiltration of humidity vs. internal generated humidity showers, dishwasher, people etc... No fan would be good to remove infiltration, but a fan helps to remove shower moisture which might change over time.

By adding a dehumidifier I assume you mean on my fan coil? Or maybe you mean a free standing unit? I'd rather have it built in of course, but not sureI have the room in my HVAC closet. The one from aprilaire looks kinda big.

[smoss]

That's interesting because it tends to be oposite of my observations...at least here in the midwest. In a static weather system... during the daytime, the radiant heat from the sun, evaporates moisture and raises the dewpoint. This is combined with evaporation from plants trying to move water up to the leaves and cool themselves. The RH of course drops, because temprature increases.

At night time, if the dewpoint approaches the dry bulb temp, which is common, you get condensation which then drops the dewpoint to a tmeprature near the dry bulb temp. So overnight temps have a limiting effect on dew point. Although most moiture is dependant on the climate and weather system. ir comming from the north is cooler and dryer, air form the south is hot and humid from the Gulf of Mexico. When they meet, you get thunderstorms. A stagnant system comming form the west over the mountians can be hot and dry.


The phenomonom you point out, may be related to air movement near bodies of water where cooler, but very humid moves off the water during the night and during the day hot dryer air comes from the land.


Please correct me if I have anything wrong.

Ok, I feel stupid here. One thing I should mention to you guys... :D I live in downtown Burlington. I am about 4 blocks from lake champlain.. :D Maybe that is important in this discussion?

FYI the lake is the next biggest lake after the great lakes. 110 miles long, 14 miles wide I think around Burlington area. No small lake... :p

[motoguy128]

Ok, I feel stupid here. One thing I should mention to you guys... :D I live in downtown Burlington. I am about 4 blocks from lake champlain.. :D Maybe that is important in this discussion?

FYI the lake is the next biggest lake after the great lakes. 110 miles long, 14 miles wide I think around Burlington area. No small lake... :p

Just go to accuweather.com and look at your hourly forecast and see hwo the dewpoint changes. http://www.accuweather.com/us/vt/burlington/05401/forecast-hourly.asp?partner=accuweather&metric=0&hbhday=1&hbhhour=12

Just as it typically does in Iowa, the dewpoint rises all afternoon as hte sun evaporate moisture frmo the groud and lakes and plants evaporate moisure during normal "respiration". In the evening, as the sun goes down, that process slows and the moisture drops.

Right now, your dewpoint is higher than mine thanks to a current weather pattern we're in... its' like San Diego weather here right now....very nice!!!. But it's still under 70F, so it's not too humid and should be manageable.

But the increased humidity in the evening, is a combination of increase occupancy along with probably washing and bathing activities, follwoing mainly by the reduce heat load causing the A/C to run less. the less the A/C runs, the less moisture it can remove.

Much much you can do other than add a whole house dehumidifier. Which I'm starting to think is a very good idea for most homes, to get comfort, and fresh air, while using the least energy.



I think it alos could be possible to use a inverter system with multiple indoor coils... and some complex linesets, to allow the system to be both a dehumidifier and an air conditioner at the same time by sometimes using 1 coil as a condenser to reheat the air just as a dehumidifier does. Combined with possibly recycling some air to dry a weat coil.... you could create the ultimate IAQ system. It's probably been discussed, but it's currently cost prohibitive given the complex lineset and multiple electronic solinoid valves needed.

[Shophound]

That's interesting because it tends to be oposite of my observations...at least here in the midwest. In a static weather system... during the daytime, the radiant heat from the sun, evaporates moisture and raises the dewpoint. This is combined with evaporation from plants trying to move water up to the leaves and cool themselves. The RH of course drops, because temprature increases.

At night time, if the dewpoint approaches the dry bulb temp, which is common, you get condensation which then drops the dewpoint to a tmeprature near the dry bulb temp. So overnight temps have a limiting effect on dew point. Although most moiture is dependant on the climate and weather system. ir comming from the north is cooler and dryer, air form the south is hot and humid from the Gulf of Mexico. When they meet, you get thunderstorms. A stagnant system comming form the west over the mountians can be hot and dry.


The phenomonom you point out, may be related to air movement near bodies of water where cooler, but very humid moves off the water during the night and during the day hot dryer air comes from the land.


Please correct me if I have anything wrong.

You are correct. I had my head around a different concept when I wrote that post. My apologies to you and the board for any apparent confusion.

For Smoss, what is likely going on is his heat gain to his condo falls off at night, so the a/c system can't run as long to dehumidify. The infiltration he's seeing is 24/7. Without actually visiting his building it's a tough call to state whether the hallway is positive in pressure in respect to his condo unit. That is often the intent of pressurizing hallways with conditioned air, so it keeps the condos pressurized in respect to outdoors, reducing infiltration of air from the exterior skin of the building. But, it sure sounds like that is what is occurring. Time on the site with a manometer and other instruments would reveal the true nature of the problem.

[Shophound]

Actually, the day before had very very similar conditions. When I woke up humidity was same, 53% and temp of 72. I didn't see much of a chance with the fan being set to auto and the fan off. Also note that I had the circ feature only programmed during the day, not at night. I did that to help reduce humidity at night when the ac runs less. I now have it set to auto 24/7. I am hoping I might see the humidity drop after a few days vs. just overnight. I know it takes a while to for humidity to change.

I am still confused about ifiltration of humidity vs. internal generated humidity showers, dishwasher, people etc... No fan would be good to remove infiltration, but a fan helps to remove shower moisture which might change over time.

By adding a dehumidifier I assume you mean on my fan coil? Or maybe you mean a free standing unit? I'd rather have it built in of course, but not sureI have the room in my HVAC closet. The one from aprilaire looks kinda big.

Infiltration of humidity comes from air forced into your dwelling via several means. For free standing houses, it is a combination of wind pressure on the building, temperature differences between outdoors and indoors, and the convective currents of air within the building acting on a building envelope (walls and ceilings) that are not airtight in respect to outdoors. For a condo building like yours these three elements are still in play, but if the hallway outside your door is pressurized with treated (or untreated) outdoor air, it is acting to force some of that air into your unit, likely through the gap under your front door.

It' also possible the hallway system is sucking air OUT of your condo, just like the bath fan is, which means whatever air is sucked out must be made up somehow. That's another component of infiltration. Whenever air is exhausted from an interior area, it must be made up somehow. I have yet to see a building airtight enough that the window panes bow in whenever someone turns on the stove exhaust or bath fan, so all buildings must leak to some extent. Yours is no exception. It's only a matter of identifying the particular dynamics involved in your case, and doing something to mitigate same.

Internally generated humidity is mostly momentary. When you're done showering, the moisture generation stops. It's then a matter of you and your shower surfaces drying off. Your exhaust fan removes the steam and water vapor, bringing in air from the rest of your condo to do it. The a/c runs and removes leftover moisture from your shower. Same goes for running the dishwasher. It's incidental. Cooking and laundry is the same.

Infiltration is continual. During the day your condo warms up from solar heating, so the a/c runs more. At night the building is radiating heat to the sky, so the heat load inside your unit falls off. The a/c runs less. Pertaining to my earlier mention of dew point, the true matter is anytime the outdoor dew point is above 55 degrees and this air is entering your home, it can elevate your interior humidity levels to where you may become uncomfortable. At night, with reduced a/c run tmies and outdoor dew points still above 55, your unit is loading up with moisture.

Try placing a towel to block the gap under your entry door tonight, and then see if it makes much difference tomorrow morning. Leave your a/c blower on auto and turn your bath fan off after you're done creating any moisture and odors in that room.

A whole house dehumidifier can be incorporated into your existing ductwork. Teddy Bear is the expert on these systems, so he would be your source here for info on that.

[smoss]

Infiltration of humidity comes from air forced into your dwelling via several means. For free standing houses, it is a combination of wind pressure on the building, temperature differences between outdoors and indoors, and the convective currents of air within the building acting on a building envelope (walls and ceilings) that are not airtight in respect to outdoors. For a condo building like yours these three elements are still in play, but if the hallway outside your door is pressurized with treated (or untreated) outdoor air, it is acting to force some of that air into your unit, likely through the gap under your front door.

It' also possible the hallway system is sucking air OUT of your condo, just like the bath fan is, which means whatever air is sucked out must be made up somehow. That's another component of infiltration. Whenever air is exhausted from an interior area, it must be made up somehow. I have yet to see a building airtight enough that the window panes bow in whenever someone turns on the stove exhaust or bath fan, so all buildings must leak to some extent. Yours is no exception. It's only a matter of identifying the particular dynamics involved in your case, and doing something to mitigate same.

Internally generated humidity is mostly momentary. When you're done showering, the moisture generation stops. It's then a matter of you and your shower surfaces drying off. Your exhaust fan removes the steam and water vapor, bringing in air from the rest of your condo to do it. The a/c runs and removes leftover moisture from your shower. Same goes for running the dishwasher. It's incidental. Cooking and laundry is the same.

Infiltration is continual. During the day your condo warms up from solar heating, so the a/c runs more. At night the building is radiating heat to the sky, so the heat load inside your unit falls off. The a/c runs less. Pertaining to my earlier mention of dew point, the true matter is anytime the outdoor dew point is above 55 degrees and this air is entering your home, it can elevate your interior humidity levels to where you may become uncomfortable. At night, with reduced a/c run tmies and outdoor dew points still above 55, your unit is loading up with moisture.

Try placing a towel to block the gap under your entry door tonight, and then see if it makes much difference tomorrow morning. Leave your a/c blower on auto and turn your bath fan off after you're done creating any moisture and odors in that room.

A whole house dehumidifier can be incorporated into your existing ductwork. Teddy Bear is the expert on these systems, so he would be your source here for info on that.


My condo door is a solid core door. It has a full sweep underneath (no gap). However, the weather stripping around the right side isn't perfect since I can see a small gap of light that comes through.

I should be able to test your theory if I leave the door partially open a smidge. Should I feel air coming in or going out? Also, I can blow out a candle or use incense to see which way the smoke blows, in our out?? That might help. I don't think I am getting any large amount of air from the hallway at least through the door that is.

[Shophound]

My condo door is a solid core door. It has a full sweep underneath (no gap). However, the weather stripping around the right side isn't perfect since I can see a small gap of light that comes through.

I should be able to test your theory if I leave the door partially open a smidge. Should I feel air coming in or going out? Also, I can blow out a candle or use incense to see which way the smoke blows, in our out?? That might help. I don't think I am getting any large amount of air from the hallway at least through the door that is.

Cracking the door open a smidge is a good way to see which way any air might be going. I don't like creating smoke unless it's with a smoke pencil, which is safer. A small piece of soft tissue (a single ply) can be used in some cases to indicate air movement. Often our own hand or skin can detect even small amounts of air movement.

If you detect air coming in, the hallway has a higher pressure than your condo. If air exits into the hallway, your condo is pressurized in respect to the hallway. I would do this test with the a/c blower off in your condo.

[smoss]

Cracking the door open a smidge is a good way to see which way any air might be going. I don't like creating smoke unless it's with a smoke pencil, which is safer. A small piece of soft tissue (a single ply) can be used in some cases to indicate air movement. Often our own hand or skin can detect even small amounts of air movement.

If you detect air coming in, the hallway has a higher pressure than your condo. If air exits into the hallway, your condo is pressurized in respect to the hallway. I would do this test with the a/c blower off in your condo.

I'll try it tonight with the blower off. I will use an incense stick. Very safe.

I am curious as to what I might find. Also, in that hallway, there is an elevator. The elevator has no HVAC. It runs to the bottom floor of the building which is a parking garage open to the outside. Maybe that has something to do with air infiltration through the elevator or the shaft. I am the furthest away from the elevator but still.

Also, to make things worse, the parking garage is enclosed except for the gate to allow cars in. There is a huge fan that runs to air out the garage when it detects carbon monoxide from cars. It rarely runs though. I maybe hear it once a month or so.. at least when I am in the garage that is. I don't spend to much time in the garage obviously. Maybe some pressuration issues with the garage elevator and fan system.

[smoss]

I didn't see any movment of air between my condo and the hallway. Maybe very very slight movement to the hall, but nothing major. Most of the time the smoke just went straight up past the slightly open door. I made sure the AC was off along with the bathroom fan as well.

I got home, house temp was 78, humidity was 54%. Unit setpoint was 78 so it was running at some point to maintain 78 even though it wasnt' very warm outside.

I did decide to close down the air vents very slightly that are located in the main living room where the tstat is. I get less air blowing around which was great for my original complaint, and all the rooms are within one degree of each other. Before the bedrooms might have been 2 degrees warmer. In any event, the AC now runs close to 20 minutes as opposed to 10 minutes before. My humiditiy did drop. As of last night, it was 72.3 in my hourse and 50% relative humidity. Outside dewpoint at that time was around 60 degrees. This morning, inside temp 72 degrees and 53% relative humidity.

So I think things are performing better. It might be better to have an dehumidifier for my situation, however, the expense is rather high compared to just paying a little more on AC. I think I feel the problem less becasue I have a good amount of heat load being in a condo. People who own homes in this area probably would benefit even more from an dehumidifier since they have little heat load. For example a home in the woods our of town where it is even cooler.

[Shophound]

The hallway may not be as much of a factor as previously considered, but since you had the bath fan off, your smoke test merely showed the hallway in itself does not appear to be pressurizing your condo through the door (or depressurizing it). If you had turned the bath fan on I imagine you would have seen the incense plume trail into your unit.

I understand the cost factor for dehumidification. Your adjustment to your living room register dampers seems effective...not the best place to perform air balancing but sometimes that is all you're given. With the net effect of your a/c running longer, you've extended the amount of time it can dehumidify.

Personally I probably would have found your previous condition of 72 degrees @ 53% RH pretty comfortable, but we're all different. My own house stays at 75 degrees/44% RH when I'm home, and when I've been sitting idle for some time it's almost too cool. All of us have variant comfort needs.