higher efficiency=less moisture?

[tdecker707]

There is a radio talk show here in Houston where the host always talks about the negative effects of having too much efficiency. He says that a high efficency split system will not pull enough moisture out of the air because it does not run long enough. I am under the impression that if a Manual J load calc is done and the system and ducts are all sized properly then the only thing that would change by having an 18 SEER system versus a 12 SEER is your electric bill would be lower and you would probably have a much quieter system. Does this overpaid radio guy know what he is talking about?
:payattention:

[saylor240]

higher efficiency=less moisture? CORRECT in some cases.... i have seen what your talking about where inccorect sizing or poor ductwork can have adverse effect...

18seer will use less energy than 12 seer correct..and Variable blower will be quieter if set up correctly and proper ductwork..and that radio guy does not know what he is talking about..high seer units with variable blower are designed and programmed to run the fan working with a humidistat spacifically to keep humidity at lower levels...he may have had poor install and just be all huffy, call him and tell him to look up the facts and change his moist diaper...

[tdecker707]

Moist Diaper, that's funny. Thanks for the tips!

[pstu]

I am a homeowner in Fulshear and get the Houston radio programs. Could you give a clue or two when I might hear this program?

Long runtimes are a function of system sizing and probably have nothing to do with SEER. There *might* be an issue with SHR, Sensible Heat Ratio but that is not what you quoted. To get the max SEER a system can be built with high SHR which means low latent heat removal -- this is all theoretical to me and I cannot promise it actually happens. It would seem to me the ideal system for Houston climate will use the highest SEER condensor component, but choose a coil which runs colder, which means more humidity removal, which means not the highest SEER system.

Best wishes -- Pstu

[amd]

He says that a high efficency split system will not pull enough moisture out of the air because it does not run long enough.

Huh?

A split system rated at 36k BTUs @ 95F/80F indoor/outdoor removes 36k BTUs per hour, whether it's 6 or 18 SEER. :rolleyes: :rolleyes:

[BaldLoonie]

As you go up in efficiency you can find less moisture removal. Varies by brand and model. For example, most 13 SEER Rheems have a sensible to total ratio of 70% meaning at ARI conditions, 70% of the capacity is sensible, 30% latent. I looked up a 16 SEER recently, on high it had a 75% sensible ratio. I've seen that in other brands too. A-S/Trane is rather low on their 13 SEER units as well. But then some brands have a 13 SEER ratio of 75% sensible so they would be no better than the high end of other brands.

Some brands on low have an even higher ratio so the time spent on low isn't removing that much moisture. So don't buy a 2 stage always expecting better humidity control.

So, as always, key is not oversizing, blower speeds below 400 CFM/ton and if going with a variable speed blower, use a VP IAQ or similar and hook up the dehumidify on demand.

[flange]

install a humidistat or iaq and use the blower to your advantage. many of these units do have a higher instance of sensible heat removal by a single digit percentage, but add the humidity control and make it do what you want. if your latent load is not real high, you can run at high speed without worry. when rh goes up, the system takes over, drops fan speed and performs dehumidification.

[Texas-Tech]

I am a homeowner in Fulshear and get the Houston radio programs. Could you give a clue or two when I might hear this program?

Long runtimes are a function of system sizing and probably have nothing to do with SEER. There *might* be an issue with SHR, Sensible Heat Ratio but that is not what you quoted. To get the max SEER a system can be built with high SHR which means low latent heat removal -- this is all theoretical to me and I cannot promise it actually happens. It would seem to me the ideal system for Houston climate will use the highest SEER condensor component, but choose a coil which runs colder, which means more humidity removal, which means not the highest SEER system.

Best wishes -- Pstu

The show is on 700am ksev on sat from 2pm till 4 i believe..called the "thirty green radio show" with a guy named Gary Parr. I listen to that station all the time and have heard his show numerous times.

He does have a web site by the same name.

[green jumper]

I am a homeowner in Fulshear and get the Houston radio programs. Could you give a clue or two when I might hear this program?

Long runtimes are a function of system sizing and probably have nothing to do with SEER.

Best wishes -- Pstu

On an a/c unit longer runtimes do help with efficency. The first 15 mins of operation for a unit is very inefficient, reducing that by sizing properly and multiple stages helps reduce your cost.

[Shophound]

If I lived in Houston and was on the radio, I'd be talking about leaky ducts and leaky buildings and stupid things done all the time that make homes and commercial structures expensive and clumsy to keep comfortable.

Number one maxim for hot, humid climates: you can't condition air that you can't contain!

Make it tight, ventilate it right. Give the building the high SEER number.

[pstu]

I am acquainted with Gary Parr and would like to give him the chance to say he was misquoted. Certainly he knows about ACCA methods and should know better than that. Used to listen to his show especially when it was just him and called "Gary on the Air", but with his recent "Thirty Green" team approach it seems to have become more generic and less interesting. For what that's worth.

Best wishes -- Pstu

[RoBoTeq]

Sounds like Gary Parr may have listened to David Debien, who also used to have a talk show in Houston. Some of David's methods were sound, for the Houston area. David and I clashed when he started telling contractors in my area his methods, which can harm equipment in my area.

[pstu]

Sounds like Gary Parr may have listened to David Debien, who also used to have a talk show in Houston. Some of David's methods were sound, for the Houston area. David and I clashed when he started telling contractors in my area his methods, which can harm equipment in my area.
David Debien influenced a lot of people in this area and was a real asset to the Houston community. I especially enjoyed his well articulated opinions which sometimes clashed with conventional wisdom. It would be interesting to hear which of Debien's opinions were a poor fit for conditions in your area.

I am actually going to defend Gary Parr in this particular thread (not to be construed as defending him in every aspect). His radio statements about improving the building envelope, are very much in line with what Shophound has said. I have not heard him dissent from ACCA wisdom, and I think if one asked him directly whether high SEER air conditioners have poor humidity removal, he would give a reasonable answer and not a half-truth. He would probably say "it depends" and follow up with truthful examples. Listening to a radio show it is sometimes easy to hear something different from what the AC guy is trying to say. Now if we were speaking about the other radio guy in the area, I have heard Tom Tynan deliver some real howlers on the subject of AC, sizing, and humidity. Tom listened to David Debien when he was alive, but he only heard the simple version and sometimes misunderstood.


Regards -- Pstu

[teddy bear]

In my humble opinion, High Seer coils operating at very cold temperatures remove as much moisture low Seer coils at the same temperature. Low Seer coils may operate a little longer because they are lower efficiency. We are splitting hairs. The biggest problem with large coils is that they retain more moisture on the coil. The moisture on the coil re-evaprates into the home during the off cycle. During long run cycles, high seer coils with correct set-up will remove a little more moisture per KW. Imagine two speed a/c with a high Seer coil on low speed. The coil ratio increases by a factor of 2. Extending the on time is some benefit shorting the off cycle. Yet during the off cycle, many lbs. of moisture re-evaporates back into the home. High/low Seer coils are unable to remove enough moisture during the low/load cooling cycle.
Most of you know where this is headed. If you want good humidity control with low/no cooling load, provide a supplemental dehumidifier. If you on a budget, a simple high seer a/c with even a free standing high efficiency dehu will provide better humidity control.
Regards TB

[Shophound]

TB, a 'high SEER" evap coil running at the same temperature as a "low SEER" coil is in essence no longer a "high SEER" coil. One of the principle reasons the higher SEER systems run higher evap pressures/temperatures is because they do so in conjunction with lower condensing pressures/temperatures. This is to reduce the compression ratio, which reduces compressor current draw, and increases compressor efficiency.

Unfortunately, a warmer evap coil will extract less moisture from the air than an equivalent coil with identical entering air conditions that is operated at a lower temperature. Simple psychrometrics...the colder a coil is below the dew point temperature of the air passing over the coil, the more moisture it will remove from that air.

It is common knowledge that a/c systems in humid climates should be operated with the indoor blower set for "auto", not "on". This greatly reduces how much moisture evaporates off the cooling coil between compressor run times.

[RoBoTeq]

David Debien influenced a lot of people in this area and was a real asset to the Houston community. I especially enjoyed his well articulated opinions which sometimes clashed with conventional wisdom. It would be interesting to hear which of Debien's opinions were a poor fit for conditions in your area.

I am actually going to defend Gary Parr in this particular thread (not to be construed as defending him in every aspect). His radio statements about improving the building envelope, are very much in line with what Shophound has said. I have not heard him dissent from ACCA wisdom, and I think if one asked him directly whether high SEER air conditioners have poor humidity removal, he would give a reasonable answer and not a half-truth. He would probably say "it depends" and follow up with truthful examples. Listening to a radio show it is sometimes easy to hear something different from what the AC guy is trying to say. Now if we were speaking about the other radio guy in the area, I have heard Tom Tynan deliver some real howlers on the subject of AC, sizing, and humidity. Tom listened to David Debien when he was alive, but he only heard the simple version and sometimes misunderstood.


Regards -- Pstu
David's ideas, which were far from being new understandings, only worked with straight cooling systems, eliminating 50% of the cooling systems in my neck of the woods that are heat pumps. David's designs are only completely effective with slab coils which there are not very many of in my area. Most importantly, David's designs were based on constant load, which in my area there is more of a humidity issue than a heat gain issue. Starting up an oversized condensing unit connected to an undersized indoor coil on a 65 degree morning is just asking for compressor failures. Those are our conditions in the mid-Atlantic area.

[RoBoTeq]

In my humble opinion, High Seer coils operating at very cold temperatures remove as much moisture low Seer coils at the same temperature. Low Seer coils may operate a little longer because they are lower efficiency. We are splitting hairs.Higher SEER coils are physically larger coils. In order for a physically larger coil to to be of the same temperature as a smaller, less efficient coil, is by reducing the amount of air crossing that coil with the same capacity of refrigeration. If you can reduce the amount of air going across the coil by using an ECM variable speed blower motor, you can achieve a greater degree of dehumidification with a higher efficiency system then you can with a lower efficiency system. There will be a reduction in efficiency in order to obtain the better dehumidification.
The biggest problem with large coils is that they retain more moisture on the coil. The moisture on the coil re-evaprates into the home during the off cycle. During long run cycles, high seer coils with correct set-up will remove a little more moisture per KW. Imagine two speed a/c with a high Seer coil on low speed. The coil ratio increases by a factor of 2. Extending the on time is some benefit shorting the off cycle. Yet during the off cycle, many lbs. of moisture re-evaporates back into the home. High/low Seer coils are unable to remove enough moisture during the low/load cooling cycle. By lowering the cfm of air there is less evaporation of condensate on the coil being done with a system comprised of high efficiency components running at a lowered air volume. A large coil with a low amount of air crossing it will wring out the moisture from the air.

Most of you know where this is headed. If you want good humidity control with low/no cooling load, provide a supplemental dehumidifier. If you on a budget, a simple high seer a/c with even a free standing high efficiency dehu will provide better humidity control.
Regards TB Agreed. If your dehumidifying needs far exceeds the ability of the much better dehumidifying HVAC systems that are available, then you either need to supplement the dehumidification or introduce heat to create a load. I have only run into this once in my lifetime in the Mid-Atlantic area I live in, and that was last year. The humidity was atrocious but the ambient temps never went above 70 degrees for over a week. I wound up turning my cooling on with a 72 degree setting on the t-stat and fired up my wood stove until it was warm enough to turn on my cooling system. Worked like a charm and we had the ambiance of the woodstover extended another week.

[udarrell]

TB, a 'high SEER" evap coil running at the same temperature as a "low SEER" coil is in essence no longer a "high SEER" coil. One of the principle reasons the higher SEER systems run higher evap pressures/temperatures is because they do so in conjunction with lower condensing pressures/temperatures. This is to reduce the compression ratio, which reduces compressor current draw, and increases compressor efficiency.
Additionally, with piston compressors the higher suction pressures result in increasing the volumetric capacity of the smaller volume piston compressors per tonnage of cooling. Scroll compressor's may not be affected as much; - perhaps a Scroll engineer will comment...


Unfortunately, a warmer evap coil will extract less moisture from the air than an equivalent coil with identical entering air conditions that is operated at a lower temperature. Simple psychrometrics...the colder a coil is below the dew point temperature of the air passing over the coil, the more moisture it will remove from that air.

It is common knowledge that a/c systems in humid climates should be operated with the indoor blower set for "auto", not "on". This greatly reduces how much moisture evaporates off the cooling coil between compressor run times.
I'm in general agreement with your statements.

One way they get a colder coil with higher SEER systems is to step-up the condenser tonnage resulting in larger compressor pumping capacity & drop the airflow to around 325-cfm per-ton.

In essence, you are using a larger tonnage compressor/condenser with the airflow & BTUH operating output of the smaller tonnage compressor/condenser.

I have witness this being done, - & it is a way to achieve increased latent capacity with on-target required BTUH load-calc, with that lower A/C's tonnage airflow CFM, - at perhaps somewhat lower EER & SEER.

As long as it is properly explained to the customer, - I am for a practice when it achieves customer comfort goals. (EER & SEER are NOT everything...) - Darrell

[beenthere]

One way they get a colder coil with higher SEER systems is to step-up the condenser tonnage resulting in larger compressor pumping capacity & drop the airflow to around 325-cfm per-ton.

In essence, you are using a larger tonnage compressor/condenser with the airflow & BTUH operating output of the smaller tonnage compressor/condenser.

I have witness this being done, - & it is a way to achieve increased latent capacity with on-target required BTUH load-calc, with that lower A/C's tonnage airflow CFM, - at perhaps somewhat lower EER & SEER.

As long as it is properly explained to the customer, - I am for a practice when it achieves customer comfort goals. (EER & SEER are NOT everything...) - Darrell

Their doing it backwards then.

No reason to oversize the condenser.

A condenser with a matched coil(coiling having the same or higher nominal BTU rating) will remove humidity fine. Without having to make a 13 or higher SEER a 10 SEER unit.

Just need to lower the air flow through the coil, until the humidity is at the desired level. And then allow the blower to come back up to speed to achieve its higher efficiency.

With thermostats that can slow VS blowers down. No reason to lose all that efficiency.

Often, a proper sized and matched system. At 400 CFM per ton, is more air flow then the house often really needs. And even more sensible capacity, then the house needs, once the humidity is down.

So it works out better to install the proper size with proper matching coil. And set the blower speed, to the CFM the house needs. And then allow a thermostat to slow the blower if and when the indoor humidity is too high. And then when the humidity is back down, the stat allows the blower to speed back up.

Gives customers the comfort, and economics they want from higher SEER equipment.

When David was doing that(5 ton condenser on a 3 ton evap). He set the blowers up for 2000 CFM. Lost a lot of sensible capacity. But gained enough latent, that even if the house temp rose above stat set point. The house would still be comfortable with the low humidity.

[udarrell]

Beenthere, I agree with your post.

I'm only referring to what some contractors appear to be doing, not that it works perfectly. From what the customers' told me, they didn't use a VS blower & just installed a single stage condenser - but a half ton larger than the old unit.

It appears they were trying to take advantage of a larger compressor to pull the suction pressure/temperature down lower for a colder evaporator coil.

When airflow is dropped to 300 to 325-CFM per-ton the sensible BTUH heatload goes down, if there is a heavy latent load that heatload will increase to meet that demand.

I would want a TXV set for a fairly low superheat, & were I the engineer a suction line accumulator wouldn't hurt anything.

It may never happen, however, if I were engineering equipment for very high latent load areas of the country I'd use a larger capacity compressor in those systems to pull the suction down for a colder E-Coil.

Of course, arguments can be launched against that, but were I in that situation I'd want a larger capacity compressor along with the VS & other features.

Without a VS & other humidity controls, when a real heavy latent load is put on those smaller capacity compressors the suction pressure & E-Coil temps will go up higher than I would want; a warmer coil reduces latent capacity, occasionally might even get above the dew-point.

The compressors pumping capacity in relationship to the latent/sensible loads determines the desirable suction pressure/temperature of the E-Coil.

When sized just right, there would be little difference in EER between runtimes but the larger compressor capacity ratio should achieve a lower % Relative Humidity.

The Electric Power Companies were a powerful lobby for smaller compressors & a little lower PEAK-LOAD situation.

The important thing with the larger compressor would be to size down for longer run times.

That is my viewpoint & it would take a lot to change it. - Darrell

[teddy bear]

Higher SEER coils are physically larger coils. In order for a physically larger coil to to be of the same temperature as a smaller, less efficient coil, is by reducing the Worked like a charm and we had the ambiance of the woodstover extended another week.

Thanks for taking the time to make your counter points to my points. I do not see any problem with making a high seer a/c a good moisture remover except more retained moisture on the coil at the end of the cooling cycle. Only one place for that to go--slowly back into the home during the off cycle.

Fortunately for me, I am encountering thousands of people who have been unable to maintain the desired %RH.
If you have adequate fresh air change in during the different weather conditions we have in most green grass climates plus the moisture from the occupants, you will have higher indoor dew points than outdoors. In the midwest, our basements need dehumidification now! The homes I monitor are removing 10-20 gals per week to maintain <55%RH. The mainfloor of the homes with good fresh air change are ok as long as the outdoor dew point is <55^F. +60^F outdoor dew points plus occupant moisture is +65%RH. We are on the edge of needing mainfloor dehumidification. When the outdoor temps are +65^F, mainfloor indoor dehumidification is needed. Avoiding all fresh air possible will postphone this for a couple weeks. How comfortable are you going to make your customers? How good is the indoor quality in a your customers home going to be? At least explain the benefits of fresh air ventilation to purge indoor pollutants and renew oxygen. Explain the benefits of <50%RH, optimum comfort and no dustmites or mold in all parts of the home. Keep a home dry with a high efficiency dehumidifier is more efficient than over-cooling with the a/c when the home is unoccupied.
Regards TB

[beenthere]

Could also be they are just installing the larger condenser. Because they are trying to match the BTU capacity of the old condenser. If they aren't changing out the evap coil.
If they are changing out the evap coil and blower. Still don't need to use a larger condenser.

Its cheaper on operating cost to use either a VS blower. Or, a fan speed control on a PSC blower to slow it down, and increase latent capacity. Only when it needs to be higher.

The money saved from not getting a larger condenser. Would help to pay for the VS blower, or fan speed control.

While using a larger condenser then the evap with a lowered air flow will reduce the condensers sensible capacity. Its sensible capacity often still ends up being more then using the right sized(AHRI listed matched)coil. And the latent increase may not be enough to remove as much moisture in the still shorter run time.

An evap coil at 35° with 600 CFM moving through it. Has the same sensible and latent capacity no matter what size condenser is attached to it.

[Mr Bill]

An evap coil at 35° with 600 CFM moving through it. Has the same sensible and latent capacity no matter what size condenser is attached to it.

I think the late David Debien might not agree with that statement, me I don't know. I like to match according to the mfg. specs on anything we do, it takes the burden off us if there is ever any issues, I learned this the hard way, many moons ago.

[Shophound]

An evap coil at 35° with 600 CFM moving through it. Has the same sensible and latent capacity no matter what size condenser is attached to it.

This would be true assuming:

a) heat load imposed on the evap coil is constant.

b) refrigerant mass flow remains unchanged regardless of condenser coil size.

c) head pressure at metering device remains the same regardless of condenser coil size.

d) pumping capacity of compressor is varied as condenser coil size is varied to maintain constants outlined in (b) and (c).

e) if (d) does not happen, even with constant air flow and constant heat load, the sensible/latent capacity proportion of the coil will vary to the extent the suction pressure is either elevated or reduced. The evap coil doesn't care how the heat is dumped once the refrigerant leaves the coil...it just wants a consistent flow of refrigerant for the given load.

Take larger commercial split systems that have unloading compressors on them (a configuration common to VFD/VAV using DX). As the heat load on the evap coil falls off, the compressor unloads to prevent the evap coil pressure from dropping below the temperature equivalent of freezing. Likewise the condenser fans either stage off or slow down to keep head pressure stable. This configuration is one way a, say, 40 ton system can be unloaded down to 15 tons or so, and still provide cooling and dehumidification to a building, without freezing the coil.

Just sayin... :D

[beenthere]

I think the late David Debien might not agree with that statement, me I don't know. I like to match according to the mfg. specs on anything we do, it takes the burden off us if there is ever any issues, I learned this the hard way, many moons ago.


He helped me design a system some years ago.

He used a larger condenser on a smaller evap.


He didn't slow the blowers down. He used 400 CFM per ton of the condenser size.

Including one system with a 2 ton evap, and a 5 ton condenser. 2000 CFM through the evap.

[beenthere]

This would be true assuming:



Just sayin... :D

Thats why I specified the evap having 675CFM and a 35° temp.

Look at evap coil ratings. They don't care what condenser you match it to. They simply list its performance by CFM and entering WB.

[Shophound]

Thats why I specified the evap having 675CFM and a 35° temp.

Look at evap coil ratings. They don't care what condenser you match it to. They simply list its performance by CFM and entering WB.

For nominal tonnage rating and system match-up purposes, this is true. My aforegoing was said in the spirit of what could happen if condenser capacity was alterred willy-nilly vs. carefully engineered.

From what I just read above, it appears David Debien (who was known on this site as Airman1) significantly oversized the condenser to the evap to get a low suction pressure, but compensated by boosting airflow to match condenser tonnage. The reasoning behind this strategy strikes me as Debien's way to assure each room received sufficient air exchange (he ran all-metal duct systems as well, IIRC) even if he was aiming for optimized latent heat removal ability. I also recall he used two stage evaps with two TXV's.

While impressive, I must wonder if he spent as much diligence and time on the building envelope, he could accomplish the same comfort results with his high installation standards applied to an off-the-shelf split system.

[Mr Bill]

While impressive, I must wonder if he spent as much diligence and time on the building envelope, he could accomplish the same comfort results with his high installation standards applied to an off-the-shelf split system.

I agree no telling what he may have accomplished, You have to remember Dave grew up as I and maybe you, where we all including the mfg's were going through some experimental years in the trade. Remember the many years of example 3-ton condensers on 4-ton coils for high efficiency systems? and hey the setup even worked well in Hot/Humid Houston I remember coming into home here with a setup like this and Lord you could hang meat inside. I think the biggest part of the reason these systems worked so well, was a 3-ton condenser actually had a 36,000 btu compressor in it. You know this was just a part of a learning experience that we all have to look back on as a good thing, that has brought us to were we are today. Dave was a mastermind at what he did, it worked better than anything else the mfg. had going on for this climate, he saw a opportunity and went for it.

Personally I think there is still places for folks like Dave to better the way complete systems perform, Dave was smart, he said the heck with all those engineers designs, I have a better idea for south Texas and he made a ton of money with his own engineering. I know the mfg. of the Compressors were probably gritting there teeth on how many warranties they might be doing on Dave's installs, but that is something probably only Al "Classical" could tell us now, my guess is probably no more than usual. I say that none of us Pro's out here should ever give up on inventing or engineering and leave it totally up to the mfg. engineers, don't forget were fighting the battle on the front lines, they are fighting it from computers in labs.

Dave was good for his generation and a very smart man and very bold to take on the mfg. and win, by a big margin in Houston, Texas, and your right his coils did have two TXV's, I have seen some of his jobs they were like 21st century stuff, that most of us only dream of doing.

[jerryd_2008]

This is very much a pro discussion and I didn't follow all of the back and forth. But the one statement below strikes me as not something people USED to do but is something that people STILL do. This is evidenced by the 5 ton coil that I had installed recently for my outside 4 ton high efficiency DFHP condenser.


... Remember the many years of example 3-ton condensers on 4-ton coils for high efficiency systems? and hey the setup even worked well ...

Does my example follow the previous methodology? My understanding is that the larger coil was necessary to raise the efficiency of the installed system.

[RoBoTeq]

Thanks for taking the time to make your counter points to my points. I do not see any problem with making a high seer a/c a good moisture remover except more retained moisture on the coil at the end of the cooling cycle. Only one place for that to go--slowly back into the home during the off cycle.

Fortunately for me, I am encountering thousands of people who have been unable to maintain the desired %RH.
If you have adequate fresh air change in during the different weather conditions we have in most green grass climates plus the moisture from the occupants, you will have higher indoor dew points than outdoors. In the midwest, our basements need dehumidification now! The homes I monitor are removing 10-20 gals per week to maintain <55%RH. The mainfloor of the homes with good fresh air change are ok as long as the outdoor dew point is <55^F. +60^F outdoor dew points plus occupant moisture is +65%RH. We are on the edge of needing mainfloor dehumidification. When the outdoor temps are +65^F, mainfloor indoor dehumidification is needed. Avoiding all fresh air possible will postphone this for a couple weeks. How comfortable are you going to make your customers? How good is the indoor quality in a your customers home going to be? At least explain the benefits of fresh air ventilation to purge indoor pollutants and renew oxygen. Explain the benefits of <50%RH, optimum comfort and no dustmites or mold in all parts of the home. Keep a home dry with a high efficiency dehumidifier is more efficient than over-cooling with the a/c when the home is unoccupied.
Regards TB
TB, I was just with a contractor today who was reminiscing about the extreme humidity issue we had last year. I referred him to come here and look you up when he asked how to determine the size of a whole house dehumidifier. I was not really certain how to answer that question, and since I also sell whole house dehumidifiers, I guess I should know as well.

[RoBoTeq]

He helped me design a system some years ago.

He used a larger condenser on a smaller evap.


He didn't slow the blowers down. He used 400 CFM per ton of the condenser size.

Including one system with a 2 ton evap, and a 5 ton condenser. 2000 CFM through the evap.
How'd that work out for our area? I am dead set against the way David designed systems if used in our lower ambient, high humidity area of the country. Seems like a huge waste of energy, taking a chance of doing damage to the compressor on low ambient operation while wiping out manufacturer's warranties if is known how the system has been installed.

[RoBoTeq]

This is very much a pro discussion and I didn't follow all of the back and forth. But the one statement below strikes me as not something people USED to do but is something that people STILL do. This is evidenced by the 5 ton coil that I had installed recently for my outside 4 ton high efficiency DFHP condenser.



Does my example follow the previous methodology? My understanding is that the larger coil was necessary to raise the efficiency of the installed system.
Those of us who are professionals in the HVAC industry are loosely using capacity designations for indoor coils. Indoor coils actually have no specific capacity. Only the outdoor unit determines capacity. We should be using more physical size or surface area vs rows of tubing terminology rather then capacity designations of indoor coils. It gets confusing for the pros, so we understand how confusing it can be for those who are not in the industry.

[Mr Bill]

Does my example follow the previous methodology? My understanding is that the larger coil was necessary to raise the efficiency of the installed system.

Your understanding is correct, this is what this trade seems to be all about these days "efficiency" and all they have done is add many bells and whistles to achieve what you could on a standard setup with a 3-ton condenser for example had a 36,000 btu compressor. Now what they do is stick maybe if your lucky a 36,000 btu compressor in a 4-ton for lower wattage usage and do everything else they can to get the wattage down and the efficiency up, and the money savings is a wash. Units now have longer run periods with more costly variable motors for better latent removal, ever price one of these variable motors to be replaced? I think the technology in going in the right direction, but when all this new stuff starts going out of warranty and the customer starts paying his on tab this is going to awake a giant. I am all for new technology but I agree with Shophound spend your money on sealing the envelope first, then you may be good to go with the old stuff. If you don't start at sealing the envelope first, all your doing with all this costly high efficient stuff is spending money to compensate for a leaky home, now how much sense does that make? Now his is just my opinion, I am sure others will voice theirs that like to sell boxes first then seal the envelope.
It's all about confusing the public now days with all this big seer stuff, matter fact I wished
they would get rid of the seer thing completely and only rate by eer. Some folks now days
have homes about as sealed as a tent, and expect there new high dollar two speed, 24 seer, variable speed, zoned system to cool there home. :gah:

[beenthere]

How'd that work out for our area? I am dead set against the way David designed systems if used in our lower ambient, high humidity area of the country. Seems like a huge waste of energy, taking a chance of doing damage to the compressor on low ambient operation while wiping out manufacturer's warranties if is known how the system has been installed.


At the last minute. They decided they weren't going to use the area in teh summer. And only installed heat.


Lots of time wasted on the bid. But learned from David.

[RoBoTeq]

At the last minute. They decided they weren't going to use the area in teh summer. And only installed heat.


Lots of time wasted on the bid. But learned from David.
I too learned from David. From what you learned, do you feel David's designs are applicable in our area? If so, are you proposing those designs to consumers now?

[beenthere]

His designs would work ok here.
But I really don't see a need to use his methods on most homes, with the availability of 2 stage condensers and VS blowers.

There are some special applications(residential homes) his designs would work very well in. And 2 stage with VS blower, does have some trouble keeping the humidity down(swamp areas, and some homes in heavily wooded areas).

You can slow a VS blower enough to have the higher latent capacity when you need it. And still allow the blower to be at normal/full CFM when the latent load is where you/the customer wants it. And not be running at a lower efficiency every time the A/C runs.

[RoBoTeq]

His designs would work ok here.
But I really don't see a need to use his methods on most homes, with the availability of 2 stage condensers and VS blowers.

There are some special applications(residential homes) his designs would work very well in. And 2 stage with VS blower, does have some trouble keeping the humidity down(swamp areas, and some homes in heavily wooded areas).

You can slow a VS blower enough to have the higher latent capacity when you need it. And still allow the blower to be at normal/full CFM when the latent load is where you/the customer wants it. And not be running at a lower efficiency every time the A/C runs.
I agree with what you state we can do without having to offend manufacturer's designs and AHRI rated systems or spend a lot more money on oversized equipment that is going to cost more to operate. Also, just how many systems in our area can we use a horizontal slab coil on? One last point, if it were up to me, I would never again use a straight cooling condenser in our area when a heat pump is more beneficial all year round. David's methods were limited to cooling only systems with horizontal slab coils.

[udarrell]

Your understanding is correct, this is what this trade seems to be all about these days "efficiency" and all they have done is add many bells and whistles to achieve what you could on a standard setup with a 3-ton condenser for example had a 36,000 btu compressor.

Now what they do is stick maybe if you're lucky, a 36,000 btu compressor in a 4-ton for lower wattage usage and do everything else they can to get the wattage down and the efficiency up, and the money savings is a wash.

Units now have longer run periods with more costly variable motors for better latent removal, ever price one of these variable motors to be replaced? I think the technology in going in the right direction, but when all this new stuff starts going out of warranty and the customer starts paying his on tab this is going to awake a giant.

I am all for new technology but I agree with Shophound spend your money on sealing the envelope first, then you may be good to go with the old stuff. If you don't start at sealing the envelope first, all your doing with all this costly high efficient stuff is spending money to compensate for a leaky home, now how much sense does that make?

Now this is just my opinion, I am sure others will voice theirs that like to sell boxes first, then seal the envelope.

It's all about confusing the public now days with all this big seer stuff, matter fact I wished they would get rid of the seer thing completely and only rate by eer.

Some folks now days have homes about as sealed as a tent, and expect their new high dollar two speed, 24 seer, variable speed, zoned system to cool there home. :gah:
Great reality based post, Mr. Bill.

That was my point about using higher BTUH compressors, I remember in the mid-1970's replacing compressors that had higher BTUH ratings than the condenser rating.

I you down sized for longer run-cycles they would flat remove the humidity, & some were matched with indoor coils fed with a TXV that you could adjust.

Also, some condenser's had accumulators to protect the compressor.

Where can I read more about David Debien? I'd like to know more about his designs, some of you appear to know about them.

I too am concerned about the higher costs, they're pricing too many out of the market. They are talking about raising the minimum seer again to 16-seer.

Our industry needs to speak out on these economic issues that could hurt everybody's bottom line - including the customer's. There are limits... - Darrell

[beenthere]

I agree with what you state we can do without having to offend manufacturer's designs and AHRI rated systems or spend a lot more money on oversized equipment that is going to cost more to operate. Also, just how many systems in our area can we use a horizontal slab coil on? One last point, if it were up to me, I would never again use a straight cooling condenser in our area when a heat pump is more beneficial all year round. David's methods were limited to cooling only systems with horizontal slab coils.

Ya, wouldn't work on a heat pump.

There are lots of people that just won't have a heat pump installed. They heard too many horror stories about cool temps from teh registers in heat mode. They won't budge, NO heat pump.

[beenthere]

Udarrel:

Go here (http://hvac-talk.com/vbb/showthread.php?t=68782) first.

Then here (http://hvac-talk.com/vbb/search.php?searchid=24807182) its a search of his post on this forum.

[RoBoTeq]

Ya, wouldn't work on a heat pump.

There are lots of people that just won't have a heat pump installed. They heard too many horror stories about cool temps from teh registers in heat mode. They won't budge, NO heat pump.
Fighting the heat pump stigma is so bad that I think we should come up with another name for heat pumps. Right now, heat pumps are the best heat source available as long and the auxilliary heat is not electric resistance.

[RoBoTeq]

Where can I read more about David Debien? I'd like to know more about his designs, some of you appear to know about them.

I too am concerned about the higher costs, they're pricing too many out of the market. They are talking about raising the minimum seer again to 16-seer.

Our industry needs to speak out on these economic issues that could hurt everybody's bottom line - including the customer's. There are limits... - Darrell
Basically, David's designs are similar to how high velocity systems dehumidify so well. By using an undersized slab coil with at least 4 rows of tubing and putting a high volume of air across it. As we know on high velocity systems, that really lowers the efficiency of the overall system. Most high velocity systems need an 18 SEER outdoor unit to achieve 12-13 SEER for the system.

David puts like a 5 ton condenser to a 2 ton slab coil with a 2000 cfm blower. By using txv's, accumulators and coil staging, his design pushes a lot of air across a coil that has refrigerant blasting through it. The coil stays cold from the amount of refrigerant absorbing heat from the abundance of air being pushed across the coil.

[Shophound]

I agree no telling what he may have accomplished, You have to remember Dave grew up as I and maybe you, where we all including the mfg's were going through some experimental years in the trade. Remember the many years of example 3-ton condensers on 4-ton coils for high efficiency systems? and hey the setup even worked well in Hot/Humid Houston I remember coming into home here with a setup like this and Lord you could hang meat inside. I think the biggest part of the reason these systems worked so well, was a 3-ton condenser actually had a 36,000 btu compressor in it. You know this was just a part of a learning experience that we all have to look back on as a good thing, that has brought us to were we are today. Dave was a mastermind at what he did, it worked better than anything else the mfg. had going on for this climate, he saw a opportunity and went for it.

Personally I think there is still places for folks like Dave to better the way complete systems perform, Dave was smart, he said the heck with all those engineers designs, I have a better idea for south Texas and he made a ton of money with his own engineering. I know the mfg. of the Compressors were probably gritting there teeth on how many warranties they might be doing on Dave's installs, but that is something probably only Al "Classical" could tell us now, my guess is probably no more than usual. I say that none of us Pro's out here should ever give up on inventing or engineering and leave it totally up to the mfg. engineers, don't forget were fighting the battle on the front lines, they are fighting it from computers in labs.

Dave was good for his generation and a very smart man and very bold to take on the mfg. and win, by a big margin in Houston, Texas, and your right his coils did have two TXV's, I have seen some of his jobs they were like 21st century stuff, that most of us only dream of doing.

Good post, Bill. Anything I said previously regarding David was not intended to sound as running him down. I respect what he did, and that he was innovative in his attempt to deal with a humid climate.

It's true...our trade, in reference to world history, is still quite young. We're just now beginning to see how important dealing with the building envelope is...even there it is slow going getting folks to see why that is important. Human beings naturally resist change. However, like David, when you stick your neck out beyond the norm, it's not only an adventure, but a rewarding one.

Personally, I sometimes find myself dreaming of ways to tweak my own residential system, to "geek it out" like David did with his systems. However, since I went after the building envelope first, the system as installed flat out rocks, so I don't find much real life motivation to change it. Still, I think it would be cool to have a system that varies its capacity to precisely match the load, both in terms of refrigeration and air flow. It would likely run a lot more quietly, and overall use less energy.

[beenthere]

How is it keeping your humidity, after all the envelope improvements.

[Shophound]

How is it keeping your humidity, after all the envelope improvements.

Right now, with windy outdoor conditions @ 87^F/44%RH (64^F dew point), at 75 degree indoor setpoint the humidity levels are running around 50%. Last summer with increased run times the RH dropped into the low to mid-forties.

[Silver06]

David puts like a 5 ton condenser to a 2 ton slab coil with a 2000 cfm blower. By using txv's, accumulators and coil staging, his design pushes a lot of air across a coil that has refrigerant blasting through it. The coil stays cold from the amount of refrigerant absorbing heat from the abundance of air being pushed across the coil.

I'm curious, did the old Westinghouse HiReLi have a high latent capacity? If I remember correctly from some diagrams, didn't those systems use a flooded evaporator? The unit was also a heat pump, correct?

Not saying it was high efficiency, but I was curious about the latent capacity.

Thanks!

[beenthere]

Right now, with windy outdoor conditions @ 87^F/44%RH (64^F dew point), at 75 degree indoor setpoint the humidity levels are running around 50%. Last summer with increased run times the RH dropped into the low to mid-forties.

Be interesting to see what your RH would be if you knocked 100 CFM off your total CFM.

[RoBoTeq]

I'm curious, did the old Westinghouse HiReLi have a high latent capacity? If I remember correctly from some diagrams, didn't those systems use a flooded evaporator? The unit was also a heat pump, correct?

Not saying it was high efficiency, but I was curious about the latent capacity.

Thanks!
I am not familiar with that system. But I've heard that you can be sure if it's Westinghouse:yes:

[Mr Bill]

I am not familiar with that system. But I've heard that you can be sure if it's Westinghouse:yes:


Yes you can.

[Shophound]

Be interesting to see what your RH would be if you knocked 100 CFM off your total CFM.

It has actually dropped toward the mid-forties (room temps still averaging 75) after I made progress patching a large hole in my ceiling next to the fireplace. Even before I patched it I could hold RH in the 50% range.

I've been fighting a chimney stone leak for a long time now. Finally turned the corner on it and am able to patch the ceiling back up.

[teddy bear]

TB, I was just with a contractor today who was reminiscing about the extreme humidity issue we had last year. I referred him to come here and look you up when he asked how to determine the size of a whole house dehumidifier. I was not really certain how to answer that question, and since I also sell whole house dehumidifiers, I guess I should know as well.

I put off answering this question until i had time to give you a thorough answer. In homes with a basement or crawlspace you need a lower dew point than in a home on a slab or more dehumidification.
The pints per day that need to be removed are determined by:
1. The dew point and volume of the infiltrating/air leakage volume which depends on the air tightness of the home.
2. The number of occupants and activities.
3. The occupants expectations of comfort.

In typical Basement/crawlspace homes 90-100 pint per dehus will provide 50%RH in 3,000 sqft of total space with 4 occupants and 75 cfm of fresh air infiltration/ventilation. In very air tight homes like the spray foam insulated, may beable to use a smaller dehu. A high efficiency air tight home may get by with a 75 pint dehu.

Roughly 50 pints of dehu for the first 1,000 sqft of home/9' ceilings depending on all the varibles. Consider 25 pints per day for each additional 1,000 sqft. of space. I suggest including the moisture load of 75 cfm of fresh as a minimum amount fresh air. This is a 3 pint per hour moisture load with 75^F outdoor dew point. During hot weather the a/c will dehumidify double this amount. During no/low cooling loads the a/c does not remove any moisture. In a 30 mph wind most homes will infiltrate/exfiltrate 150-200 cfm of fresh air. This will momentarily exceed the drying capacity of the a/c and dehu. Do not size for the extreme as these load rise and fall over several days. +65%RH for extended periods will allow biological growth like dust mites and mold.
I prefer combining fresh air with house air, passing throug a merv 11 filter via ventilation dehu back to the home via heating/cooling ducts. The dehu will only operate when the indoor %RH exceeds the desired interior %RH. High cooling loads with a properly set-up a/c will remove enough moisture to keep the indoor %RH less than 50%RH. As the cooling load declines, the %Rh will exceed the 50%RH setting and the dehu is activated. Fresh air is only need when the home occupied. An occupancy timer or CO2 controller will avoid over ventilating when the home is unoccupied or the wind is blowing.
Dealing with occupants who desire very low relative humidity or high volumes of fresh air, need special attention to the design of the dehumidification system. Keeping unoccupied homes dry during the wet times of the year in the SE U.S. takes about the same capacity because the holding temperature is higher and the absence of fresh air ventilation.
I welcome any further questions. Regards TB

[jerryd_2008]

.. +65%RH for extended periods will allow biological growth like dust mites and mold.
...

TB, the 65%RH kind of threw me. Seems like most here recommend <50%RH to control vermin. Even your message at the bottom of your posts mentions 50%RH.

Since I have a hard time getting the RH down below 50% and keeping it there due to the relatively high 78-79 AC temp the wife is comfortable with, this is an interesting statement to me. Can you clarify?

Thank you.

[Shophound]

Black mold thrives in dark areas in temperature ranges between 50-90 degrees and relative humidity levels >65%.

Dust mites prefer relative humidity levels above 50%.

Most humans find relative humidity levels at normal room temperatures that are below 50% and above 35% to be comfortable. Generally, the cooler you prefer your room temperatures to be, the drier your air should be, for summertime cooling purposes. It can also hold true for warmer temperatures, in order to keep mold in check.

[pstu]

There is a radio talk show here in Houston where the host always talks about the negative effects of having too much efficiency. He says that a high efficency split system will not pull enough moisture out of the air because it does not run long enough. I am under the impression that if a Manual J load calc is done and the system and ducts are all sized properly then the only thing that would change by having an 18 SEER system versus a 12 SEER is your electric bill would be lower and you would probably have a much quieter system. Does this overpaid radio guy know what he is talking about?
:payattention:
Clearly the OP heard differently but... suppose what Gary Parr really said was something like:
"A new high-efficiency system will tend to remove less humidity because the things done to maximize SEER are things that hurt humidity removal".
From what professionals have said, would that not be supported by the facts?

It would take a real blind spot for a professional to claim that high SEER means shorter runtimes, and although that was reported by the OP that does not seem like something Parr would actually say. Too bad he is not online to defend his words.

At the same time I am not forgetting the words of a certain guy in the Carribean, who reports that the dominant factors include not SEER but having a tight house in the first place. And he employs supply-only ventilation thru the AC system which tends to pressurize the house with filtered and conditioned air. That would testify it may be varying degrees of futile to regard the AC as the solution to many humidity problems in the first place. That is what I read into the many posts on the subject.

It would seem the optimum system for a hot-humid climate, is NOT the one with the highest SEER or EER. It may well be called a "Trane XL20" but would be configured with lower airflow and perhaps a coil which delivers SEER well below the biggest number available. Would you agree with that observation?

Best wishes -- Pstu

[Shophound]

At the same time I am not forgetting the words of a certain guy in the Carribean, who reports that the dominant factors include not SEER but having a tight house in the first place.

And some other guy in North Texas prattles on about "building envelopes" all the time on here...hmm, what's up with that?? :D


And he employs supply-only ventilation thru the AC system which tends to pressurize the house with filtered and conditioned air. That would testify it may be varying degrees of futile to regard the AC as the solution to many humidity problems in the first place. That is what I read into the many posts on the subject

A/C is only part of the overall picture. You can't dehumidify if you have no means to dehumidify, so we need the a/c. What is mostly done in humid climates , however, is an a/c set against an uphill battle. Let's tick off a few bullet points:

Air ducts in a ventilated attic in a hot climate. How foolish is this? Not enough room in the universe to quantify it.
An attic that gets hot in the first place. See remark about universe and room.
Penetrate the ceiling between this overhead oven and the spaces the occupant hopes to cool, and then don't seal them.
Put not only ducts up in the attic, but the air handler as well. And do nothing to air seal either one.
Build houses with tall ceilings with large areas of glass that are unshaded and happen to face east, south, or, worst of all, west.
Realize all the above is true and resign to it by fretting over SEER ratings and doing nothing else.


It would seem the optimum system for a hot-humid climate, is NOT the one with the highest SEER or EER. It may well be called a "Trane XL20" but would be configured with lower airflow and perhaps a coil which delivers SEER well below the biggest number available. Would you agree with that observation?

Best wishes -- Pstu

I would say go with the highest SEER one can afford, properly sized for an improved envelope.

[pstu]

So you do not believe the very top SEER matches get that way by compromising SHR?

Best wishes -- Pstu

[teddy bear]

TB, the 65%RH kind of threw me. Seems like most here recommend <50%RH to control vermin. Even your message at the bottom of your posts mentions 50%RH.

Since I have a hard time getting the RH down below 50% and keeping it there due to the relatively high 78-79 AC temp the wife is comfortable with, this is an interesting statement to me. Can you clarify?

Thank you.

Sorry about the expression of the highest possible %RH that is acceptable. My <50%RH rule includes a safety factor for carpet on concrete and growing dustmites. Occasional short excursion of high humidity is not the end of the world. If health is involved, use the saftey factor. These a/c contractors are not as concerned as you are. Nothing wrong your with your concern, in fact to your credit. I am becoming more aggressive on the amount of space a given dehu will provide comfort. Mainly because homes are more air tight now than a couple years ago. Thank for you using good dehus and comments. Regards TB

[Shophound]

So you do not believe the very top SEER matches get that way by compromising SHR?

Best wishes -- Pstu

It depends if, what I'll call the latent heat ratio (LHR..if we have a SHR, why not a LHR? A ratio has two sides, not just one) is sufficient for the dwelling at design load and happens to be a high SEER system, wouldn't this seem to indicate it's not a given that high SEER systems have compromised latent heat capacity?

That's where I'm going with my continual emphasis on the building envelope. If the envelope is tight, the moisture load is less, across the board. The tighter the structure is, the more both the latent and sensible gain spectrum slides toward internal gains vs. external gains. Most homes in humid climates load up with moisture from outdoors, less so from indoors (although certainly the internal gain is in no sense negligible).

If required fresh air make-up is brought in through controlled means vs. willy-nilly through a leaky envelope, you're going to have a lower latent load for the house interior, period. Internal latent gains are largely incidental, varying with indoor activity levels and types. You take a ten minute shower and throw about a pint of moisture into the air; a/c comes on and pulls that out within a cycle or two. You cook dinner and add another pint or so...it's removed after a cycle or two. The more constant loads are infiltration and human respiration/perspiration, along with any plants, pets, or aquariums in the house.

Human respiration/perspiration and infiltration...the latter is controllable, the former varies with indoor activity. Hence, focusing on the latter is a wise strategy for hot, humid climates, as typically it is the largest source of moisture gain to a structure's interior.

Bottom line: high SEER systems that struggle to keep a house dry when there's sufficient heat load to run the a/c system regularly likely have too much moisture infiltration into the structure for the system to handle. High SEER systems can also be crippled by poor installation, which happens all the time. I'd put blaming the equipment very low on the list, as the much higher bullet points would be building envelope issuse and installation quality.

How many times do we read on this very board how higher SEER systems were never set up properly by the installers? It's ridiculous.