Great site - tough not cooling question - long

Great site! Yet another not cooling question but its long. Any guidance appreciated... just don't say call in pro as I've done that to death.

Background -8 year old house, well insulated - low E glass throughout but, lots of it! including 6 skylights and vaulted ceilings. 2600 sq. ft. but more like 3400 sq. ft. if you consider room volumes- -basically an HVAC nightmare.

Being an engineer, I had my contractor, AND the supply house AND the manufacturer confirm equipment recommedations (which sounded inadequate to me). I believe the method used was IBR. The system is a Teledayne Laars hydro air - 1 hydronic boiler, 2 air handlers and 2 condensing units (spilt systems). Each air handler has a hydronic coil for heating and a seperate cooling coil (this is a conventional r-22 cooling system, not a chilled water system). High/Low returns in all rooms, fully insultaed duct work with velocity calcs done during sizing. Not a cheap system! Total system capacity recommended was 125k BTU heat & 5 tons cooling (2.5 up & down). I questioned both but was re-assured the science was right... trust it.

Well they were partilly right. Heating is fine, cooling has never been! Well at least not upstairs. Downstairs zone is acceptable but the upstairs zone can't keep up. Call backs always brought the same response - "you bought an ir conditioning sytem, not a refigeration system". The premise being that "slow cooling" is better than "fast cooling" for comfort... "its normal that if you turn the system on at mid day, it will not bring the temp down til after sunset becuase it need to get the humidity out first". The system needs to run 24 hours... you can't shut it off and turn it on when it gets hot! BUT, even leaving it on all the time, upstairs looses ground during the day sometimes getting 10 deg. F over set point during very hot days with all the shades drawn!

After a couple years of this same bunk and getting nowhere, I called another company in and without doing anything, they said "systems too small"... I dind't like the off the cuff answer and some others but got much the same...a guy that looks around the house, doesn't pull a panel or use a probe...perhaps they put a gauge set on the condenser and start with the "maybe this or maybe that" but no conclusives and the cath all "the syetms too small". When told that the calc were done by 3 different sources using IBR, they just shrug and smile as if to suggest experience is better than those fancy figures (who am I to argue... I'm the one with the problem).

The real problem - Laars no longer supports cooling -just heat so my air handlers are orphans. The cooling coil is 31K BTU and I can't get a larger one - I'm not even sure a larger one woould help as I think I may also have an air flow issue. To replace the air hadler altogether is tough becuase of the heating side and attic location.

any suggestions on improving the system and keeping the handler? Perhaps a 3 ton condensing unit coupled with trying to get more air flow through the handler...?

How about adding another split system ( 1 ton?) or if additional ductwork is a problem, a mini-split? It does sound like your under-sized, but can't be sure from here.

It's practically impossible to figure out what the problems are without seeing the system. It could be the load calcs missed something, or the equipment/ductwork wasn't installed correctly.

I know you don't want to hear it, but you do need to call in a pro. It doesn't sound like one has been there yet :(
No pro is going to make an assumption with only a set of gauges. A little bit of psychrometrics and air flow measurement may be required to determine if the system is working up to par. It doesn't sound like that has been determined yet.

A pro will also be able to advise you on what equipment may be retrofittable into your install, should that be required.

Obviously, if a pro determines that the equipment is working to capacity and can't get the job done, a new load calc will be required.

If the upstairs unit is working properly, there must be one heck of a load up there. I don't know what the floor plan or distribution of load is per floor, but a 2nd floor unit equal in size to the 1st floor system is usually adequate for a "typical" floor plan. Most installs in my area have smaller units cooling the upstairs.

You didn't state what part of the country you're in, or if there is an attic, and if the ductwork to the upstairs unit is in the attic.

There is a great deal of truth in what company #1 told you. With properly sized systems, you can't expect to be able to turn the systems on in the heat of the day, nor can you attempt to cool the upstairs to an acceptable level without the help of the downstairs unit. Both thermostats should be set at similar temps at the same time. If the upstairs unit is running by itself, and is properly sized, it's going to lose the battle.

What is the summer design temp where you are, and what temp are you trying to maintain?


[Edited by midhvac on 06-16-2004 at 05:50 PM]

How about some #? Like sensible heat load ,latent load,
and what seer equipment you have.

Like others have say you cant expect to turn a ac on only
doing the heat of the day and think it going to drop the sensible load in no time at all.
If you want that type of recovery,the system would have to be oversize and then it all goes wrong from there.

The heating system is it also heating domestic hot water as well? What type of boiler one thats contain alot of water,or very little?

I have seen some hydronic coil be nice and hot from bad checks,and add to the load.Thermal cycling.

simple solution from stupid people who do not know what is wrong or scared because they under sized your system.

turn it on real cold in the morning and it will keep up better or just wait till fall then it will cool.

is this a boiler or domestic water as well?

IS the boiler still keeping water hot? while in heating mode. this might sound like a stupid question but sometimes the right one.

Are you getting thermosyphoning meaning the hotwater is in the heating coil while your in heating mode.

This sometimes has been the case when using combo heating

Also if you have 2 return air ducts in each room 1 high 1 low, this seems very redundant to me.

Hot air rises cool air falls, so the cold air that falls should remain on the upper floor, but if you have a return air in all rooms the cool air is getting sucked back into the furnace and recycled.

Try blocking off the return airs in the floor (sounds like you might have too much return air

normally couple high wall R/A is enough upstairs

Midvac and others,

I agree that I needed a "pro", I certainly spent the money for one. Everyon ein the phone book says there a "pro" but finding a real "pro" in my area appears elusive... most guys I've had out are insulted when I ask pointed questions and they relaize I know enough to know they are unprepared. They usually snip at the insinuation and are quick to remind me that they are the "pro's" and can diagnose without all the fancy "toys". But, they end up being "seat of the pants" or rules of thumb types nad charge as if they weren't. The original installers at least talked the numbers and seemed to have some science behind their madness. True profesionalism is gone, now these companies hire cheap labor and rack up billable hours for guys that know less than I do. This is why I'm so soured on the "pros"... I don't mind spending the money if there is value in it but paying top dollar for what I'm getting, stinks.

To answer some questions. I'm in the northeast, MA to be specific. My cooling needs are quite modest. We keep both the upstairs and downstairs set at 75 degrees. As of yesterday, the units had been on for 72 hours straight. Yesterday I got up, both units were off becuase the house was at temp. According to the news, it only got to 82 degrees outside yesterday. when I got home, my downstairs was at 75, my upstairs was at 78. Even worst... by nine 9PM, the outside temp was in the 60's and the upstairs temp was still at 76! That unit didn't shut off until almost 11 PM!!.... it would have been faster to open windows, but I didn't.

This air handler is in the attic as well as all 2nd floor ducts. Each room (except baths) have 2 ceiling supply ducts and 4 wall returns (2 low plus 2 high). All ducts are rigid insulated except for a few that due to loaction were done in insulated flex. As far as numbers go, I haven't gotten pre and post coil temps since last year but if memory serves, the delta was low (only around 10 degrees at the closest registers). I will need to check it again becuase the pros don't. The last "pro" I called in was here just this Tuesday... all he brought was a manifold guage and a receipt book. He was here less than 30 minutes at mid afternoon when it was around 86 degrees outside. Pressures were 275 high side, 70 low (but spiking to 80-90 psi on occasion). He told ME to clean the condensing coil, "the units too small"... gave me a quote to install a 3 ton condensing unit using the existing 2.5 ton evap coil and charged me $75. I asked about the low spikes and he siad condening unit may be going, might be some moisture in the lines but no definetives.

I would love to find a guy that had ahlf the knowledge that I see on this forum.. if anyone knows of one, please share. In the mean time, I'm lloking for ideas or things that I can do tomake it better or at least understand the true cuase of my problem.

Sorry... forgot to answer a couple of questions. The boiler design is a low volume high velocity on the heating side with a seperate domestic tank fed off one zone (like a boiler mate but built in. The heating side in the heat exchangers is independant of the domestic side (fed by individual pumps pushing a 50/50 propylene-glycol / distilled water mix). The heating coils are not couter-acting the cooling or back flowing... but good thought!.

Adding another or changing out the system is always an option but not one that makes sense at this point. I'd like to know what the problem is first, before I take corrective action.

I really want to understand where the problem is so I need to know whatI should be looking at... temp drop acroos coil, air velocity, temps vs pressure. What is sub cooling? Once I have a better understanding, then I can make some better decisions. In the mean time, here's some of my ideas to help... please comment, add or subtract.

1) Clean evap and heating coil in attic handler.
2) Clean handler fan and look into a higher rpm motor for the unit (try to get some more cfm accross coil)
3) Upgrade codenser to 3 ton If I can get more CFM across 2.5 ton evap coil.
4) Install attic fan to lower temp in unconditioned space
5) Do a better job sealing all holes in attic air handler (maybe drawing in some attic air into return ?)

Now there's no doubt that you haven't had a pro out. Checking refrigerant levels and performance isn't possible with a dirty condenser. Adequate air flow across both the indoor and outdoor coils is mandatory for testing.

It's very difficult to pinpoint problem area(s) without seeing them. We could give you a few things to check, but they would require the use of testing instruments.

In your case, I would want to know the following:

Refrigerant pressures and outside dry bulb temp at which they were taken.

Evaporator entering wet bulb and dry bulb temps.

Evaporator exiting " " " " " "

The temp at the thermostat in which these tests are being done.

Temps of outdoor refrigerant lines within 6" or less of the point where the refrigerant pressures are being taken.

There's also a very good chance that high attic temps from solar gain are playing a factor, especially when the ductwork is in the attic. If I were you, I would take a very hard look at the attic ventilation design and at the condition of the ductwork there. You could be heating up either or both the supply or return air up there.

It's also possible that the attic ventilation wasn't done properly with the proper size, location and ratio of entering to exiting vents or that insulation or obstructions are blocking the vents. If solar heat gain is part of the problem, as I suspect it might be, then these problems may become apparent in the above mentioned test measurements.

Obviously attic insulation is always another possibility, due to heat gain through the ceiling into the conditioned areas. Keep in mind that insulation won't have that much effect on the attic ductwork.

I have problems myself with inadequate attic ventilation, and know that the vents are inadequate in size. I also know that the insulation is sub par.

A while back I went to Sam's Club and bought an electronic thermometer with a remote sensor for about $30 (SkyScan brand.) I have the remote sensor hanging in the attic about halfway between the roof and floor of the attic. Typical temperatures there on a sunny day have been up to 40 degrees warmer than outside temp.

I'd be in *big* trouble if my ductwork was in the attic :D

This would be another thing for you to check.



[Edited by midhvac on 06-17-2004 at 10:01 AM]

Midhvac, Thanks for sticking with me!

I believe your on the right track with attic solar gain. My options up there are limited though. Since my second floor cilings are all vaulted , the attic space is very, very limited! What space there is, is taken up by ducts/handler etc. Attic vetilation is convective loop only - soffit vents\ feeding baffles above the insulation batts and ridge vents. Currently, there is no forced ventilation and the air handler sits above the insulation so it is truely unconditioned space. The temps up there are easily 20-30 degrees above ambient outside temps. BUT, the desingers knew this going in and supposedly calculated that in (NOT). Also, the air handler cabinet is not insulated... probable for ease of access??.

I believe the duct design is good... most comment that the install must have cost a fortune becuase of the number and design of the ducts. I know I asked for the best system possible becuase of the houses layout, that both heating and cooling were dependant on the ducts and I knew that the heat stratification would challenge the system.

I can take readings and don't mind buying tools... (I kind of like tools). When you say "dry and wet bulb" temps... what is that? Are you descibing a temperature reading device or a surface temp (location) on the system? I have been using a DVM with thermocouple to get register temps... is that not the right instrument?

Also, can you describe "sub-cooling"... I've heard the term but don't understand it.

BTW - Thanks for following up... I know this is a boring read!

I can take readings and don't mind buying tools... (I kind of like tools). When you say "dry and wet bulb" temps... what is that? Are you descibing a temperature reading device or a surface temp (location) on the system? I have been using a DVM with thermocouple to get register temps... is that not the right instrument?

Also, can you describe "sub-cooling"... I've heard the term but don't understand it.

Dry bulb temperature is a normal air temperature reading; more technically speaking it is the sensible heat content of the air.

Wet bulb temperature is the equivalent of taking a dry bulb thermometer and placing wet cotton material over the bulb and allowing the wet cotton to cool the bulb by evaporation. The amount of evaporation will be determined by the humidity in the air; faster evaporation = greater cooling = less humidity= less of a temperature drop on the thermometer.
A sling psychrometer can be used for this, but you can also fashion a straw with cotton and place a temperature probe inside the cotton through the straw. Best reading is obtained when the sensor and cotton array are in an airstream, such as the main return plenum at your air handler, or closest return air grill to air handler.

These two measurements are important to HVAC technicians in that it helps determine how well the system is handling both sensible and latent heat loads. It is also important in measuring system superheat, or the amount of heat the refrigerant absorbs beyond its saturated vapor temperature (temperature at which refrigerant boils in the evaporator). Superheat is measured at the condensing unit suction line about 6" from the compressor or service valve fitting. An approximate superheat reading can be obtained by subtracting the difference between saturated vapor temperature and the suction line temperature at the condensing unit, but a superheat chart is best for doing the check exactly.

Subcooling is the amount of heat removed from the liquid refrigerant in the condenser from the point where it completely reverts to a liquid state inside the condenser (saturated liquid temperature) to where it leaves the condenser and is returned to the evaporator through the liquid line. If your system has an expansion valve, the charge is checked by subcooling, as an expansion valve is designed to maintain a steady superheat when the charge is adequate.

I'm sorry you haven't yet had a technician or pro out to your home that has taken the time to thoroughly investigate the performance of your system. My approach would be to ensure that what is installed is working the absolute best it can before I would start talking about undersizing, etc. It's just lazy to blame the installation without mounting up a good case for it.

Shophound,

thanks for the detailed explanation.

I would presume that the wet bulb measurements require some amount of time as evaporation and its cooling effects would be dependant on air flow over time. Also, wouldn't the plastic straw provide a thermal barrier to the dry bulb probe that would also reguire time to saturate? Are sling psychrometers terribly expensive? It seems like they may offer more reliable measurements?

I now understand subcooling and superheating (the definitions anyway) I'm sure the physics are beyond me at this point.

When you talk about temp measurements 6" away.... I presume your asking for "line surface temp"... (you obviously can't get inside and the surrounding air temp would be useless?) Do you just rest a dry bulb on the line and let it settle or there a special tool to do this?

BTW. I think my cooling coils are of capillary tube design, not expansion valve.

I here you on the lazy part but I think its beyond that. Refigeration theory is high tech! Many refrigeration contractors aren't keeping up with the engineering side of things. Their goal is running a business and making money. Its one thing to sell someone on your company to get a job, its another to employ this type talent to service calls. There MIGHT be guys in my area that are this good, but they certainly aren't getting dispatched on these types of calls and I'm tired of paying as if they were.

jav, my bad that I didn't catch you were using a DVM with a thermocouple for temperature measurement. This is absolutely fine for what you want to do. The trick with the straw and cotton is just a MacGyver approach in the absence of the proper tool, but it works. You merely thread the thermocouple up through the straw until it emerges into the damp cotton. The reading you are after is best obtained with a steady airflow over the wet cotton. The suction found at a return air vent would give you this.

In your case, unless you have a set of gauges and EPA certification, placing gauges onto your system is the other half of the superheat/subcooling equation. You must know at what temperature the vapor in the condenser is vaporizing at in order to calculate superheat. Same for subcooling, except you're dealing with the condenser. The pressures and temps are relative, so say if you're running a 68 pound suction pressure in the evaporator, the liquid refrigerant being injected into the evaporator through the metering device is boiling into a vapor at 40 degrees.

When you talk about temp measurements 6" away.... I presume your asking for "line surface temp"... (you obviously can't get inside and the surrounding air temp would be useless?) Do you just rest a dry bulb on the line and let it settle or there a special tool to do this?

Taping your thermocouple probe onto the suction line with black electrician's tape works fine.

BTW. I think my cooling coils are of capillary tube design, not expansion valve.

You haven't mentioned any freeze-up problems in your posts (unless I missed it). Reason I mention that is I'm wondering about the airflow through your system with two coils in the airstream; one for heating and one for cooling. I would think the design would account for the restrictive factor due to air passing through one coil before it reaches the other, reducing CFM.
At any rate, if airflow is adequate, you could have a refrigerant charge imbalance. Fixed orifice systems are notorious for being overcharged, since few techs master an understanding of superheat and subcooling. I myself was taught the "beer can cold" method, or the "charge until you get this pressure and that pressure" method. I was taught wrong and did it wrong until I forced myself to learn it differently. A tech's life would be a LOT easier if he'd master these parameters.

Refigeration theory is high tech!

Amen! Someone out there understands this! :)