Small load, small SHR

[oldfella]

What would be the best central heat pump for a very small load ( 2 tons ok, 1 ton would be best) very low SHR .5 (high latent load), and centrally distributed. Energy usage should be as low as practical.

We are building a super insulated passive house for mixed humid climate (Philadelphia). The high insulation and reduction of solar gain means that it has relatively little sensible load. It's a pretty big house and the floor plan is not open, so we are reluctant to use a mini-split unless we can connect it directly to the air distribution.

Anything come to mind? It seems hard to find SHR (sensible heat ratio) numbers on the web, is there a good source for this?

Thanks!

[sktn77a]

Rheem post theirs for their condensers/heatpumps in the "specification sheets" but I think you find the ratio is similar for the different models (3:1 - 3.5:1).

[amd]

Get a 1.5 or 2 ton unit with a TXV and ECM blower motor.

Have the installer set the blower speed below 400 CFM per ton (might be able to go as low as 300/ton) and charge it accordingly. A humidistat can be added to slow down the blower even more during periods of high humidity. Note that a freeze-stat might be required on the indoor coil to prevent compressor damage.

I doubt that you'll be able to find anything with a SHR below 0.7 at rated conditions/airflow.

The only manufacturer I know of which makes a 1 ton a/c is york. A dehumidifier might be required in mild weather.

[oldfella]

Thanks, that sounds right (detuned Heat Pump & dehumidifier). Just didn't want to miss something that would hit the nail on the head.

This is an interesting idea:
http://www.aaon.com/product.aspx?id=6

It combines a reheat function, so you can use the heat pump as a straight up dehumidifier.

[amd]

If you must get a heatpump, disregard my previous post. Insufficient airflow will absolutely kill efficiency in heating mode and possibly cause compressor damage.

[beenthere]

A York E1RD018S0 with a AHP18 air handler will get you down to a SHR of 63.

[ebierley]

Look at the inverter minisplits like Mitsubishi. They have ductable units that may work for you.

[Shophound]

What would be the best central heat pump for a very small load ( 2 tons ok, 1 ton would be best) very low SHR .5 (high latent load), and centrally distributed. Energy usage should be as low as practical.

We are building a super insulated passive house for mixed humid climate (Philadelphia). The high insulation and reduction of solar gain means that it has relatively little sensible load. It's a pretty big house and the floor plan is not open, so we are reluctant to use a mini-split unless we can connect it directly to the air distribution.

Anything come to mind? It seems hard to find SHR (sensible heat ratio) numbers on the web, is there a good source for this?

Thanks!

Your super insulated house....as you say your sensible load, at least from exterior sources, won't be equivalent to a conventionally built house. On the same note, your latent load will also differ, as you won't see nearly as much of it coming from outside due to infiltration.

With well insulated homes, internal heat gains, both sensible and latent, are much more in focus than normal. Peak latent loads will be more or less intermittent, depending on household activities, whereas with leakier homes during warm, humid weather, latent load is more ongoing, again due to infiltration.

Personally I would run a thorough heat load analysis on the home and install equipment based on that analysis. The old rule of thumb regarding oversized a/c and diminished humidity control is not the same with tight houses. My own home is considerably tighter than when I first bought it, and right now it is downright soupy outside...dewpoint is 71 degrees with sensible temperature at 76. Pretty sticky. Inside? I'm able to hold around 56-57 degrees dew point with short run times on my a/c (sensible temps running around 73-75 as system cycles). Not much sensible load on the house from outdoors right now...it's night and cloudy, yet my a/c still cycles enough to keep humidity levels in check (could be a tad drier but we are not uncomfortable and we're not growing mold on the walls with these conditions).

All that said to say my a/c is essentially oversized for the current conditions imposed on my dwelling, but my indoor environment is manageable. While I still do not recommend oversizing a/c equipment, the walkaway lesson here is that for tight, well insulated homes, the old rule of thumbs don't necessarily apply.

[teddy bear]

Avoiding fresh air ventilation decreases the moisture load in a home but your home ends up with lousy indoor air quality. When a home is occpied, you need an air change every 4-5 hours. In a high quality home, provide mechanical fresh air ventilation. These H_AC (no Ventilation) guys do not recognise the value of fresh air because they are unable to provide good humidity control during cool wet weather. For the best indoor air quality, check out whole house ventilating dehumidifier. Provide fresh air when the home is occupied and provide <50%RH regardless the weather or with or without a/c operation. Regards TB

[beenthere]

These H_AC (no Ventilation) guys do not recognise the value of fresh air because they are unable to provide good humidity control during cool wet weather. Regards TB

That sounds like a dehumidifier salesman. That just wants to sell dehumidifiers to people weather they need one or not.

If he builds his house right. He won't have that high latent load he describes.
Unless he brings in more fresh air then he needs.

[Shophound]

Avoiding fresh air ventilation decreases the moisture load in a home but your home ends up with lousy indoor air quality. When a home is occpied, you need an air change every 4-5 hours. In a high quality home, provide mechanical fresh air ventilation. These H_AC (no Ventilation) guys do not recognise the value of fresh air because they are unable to provide good humidity control during cool wet weather. For the best indoor air quality, check out whole house ventilating dehumidifier. Provide fresh air when the home is occupied and provide <50%RH regardless the weather or with or without a/c operation. Regards TB


And I say tailor the ventilation strategy to the local climate and building type, use, and layout.

For humid regions, introducing untreated fresh air into the structure is counterproductive. Yes, we need to ventilate. That is not in dispute, nor should be by anyone concerned. The focus is on what is the best way for a given climate and structure. Ventilating dehumidifiers can be one way, so can a correctly balanced ERV. For my neck of the woods, fresh air intake on the a/c return can work, given our window of "cool, wet weather" is rather short.

And... I don't sell anything. I'm only interested in methods that work the best for a person's given budget and health/comfort needs, do not hazard the building, and do not waste energy needlessly.

[Carnak]

If the SHR is truly that low you will need reheat. Means a dehumidifier

Would have to run your AC on 100% oustide air to get that low of an SHR.

I am a little skeptical of the SHR obtained.

[Shophound]

If the SHR is truly that low you will need reheat. Means a dehumidifier

Would have to run your AC on 100% oustide air to get that low of an SHR.

I am a little skeptical of the SHR obtained.

If the house is as tight as is advertised, where's the moisture coming from? Internal gains can't be so high as to kick the SHR down to .5??

In my own area, normal stick frame construction averages around .9 on a Manual J. At design we're about equivalent with Philadelphia on btu/lb, just a tad drier on the gr/lb difference at 22 vs. 38 for Philly.

A super insulated house just gotta have some amount of internal sensible gain. Refrigerators, electronics, laundry, lighting, cooking...the more insulated the more internal gains affect heat rise within the structure. Carnak's own tropical island attic, insulated at the roof line, heats up AT NIGHT because of his ceiling lights being lit. Unless these people have a hot tub in the basement (like my brother's house in Bucks County did), if infiltration is practically nil, there's enough internal latent heat generation to drive the SHR down to .5?

Internal moisture generation, apart from plants, pets, and people, is intermittent at best. You don't shower all day or do laundry seven days a week, and if you're cooking and showering and laundering without ventilating the spaces where these moisture sources arise, you're just asking to live in a swamp.

[Carnak]

A great big volume with a small air change rate can mean a lot of moisture to get rid of. A mansion with a 0.1 ACH could say have the same infiltration measured in cubic feet per minute or hour as say a small house with 0.5 ACH.

The last man j program I looked at gave me warnings on about every single room that I really needed a VAV system. Seems to be too scared it will over size and cuts back on the gain of the glass. Seems to say "when you get direct sun this room will get on the hot side so we are going to size it so it gets warm for a couple hours". So the sensible load carried in the calculations seems to be lessened for fear of 'over sizing' because over sizing is deemed a real bad thing to do.

Manual J has you thinking all the time about 'how many more grains are in the outside air, compared to how many grains you want inside the house'.It sort of looks at how much moisture you have to remove from the room air to compensate for the extra mositure the infiltration is bringing in.

So this is not the best train of thought because it is almost the same thing as saying, let's let all this mositure into the room air and then squeeze blood from a stone and super dehumidify air that is already supposed to be dry.

So my school of thought is lets get outside air to the coil first and dry it out ahead of time. So we have some more humid air going into the coil, the SHR of that coil is going to drop (it ain't dropping to 0.5). Your entering wet bulb goes up closer to that infamous 67 so you are starting to get closer to the capacity it is rated at.

Anyways you can easily get this mixed air down below the dewpoint you want to maintain. How much below, I don't think it really matters its not like you have a Pentacostal Congregation worshipping in your home.

If you have air with say a 54 dewpoint being supplied to a space, and you are pressurizing a space, it means that air with a dewpoint higher than 54, like say 55F is being purged out of the house.

The mositure in that exfiltrating air, is going to be about what occupants will generate. Its almost like having open windows in Arizona when you are running a swamp cooler, you let the air out so that the humidity does not build up.

Do some math, figure out how much mositure is in 50 CFM of air at 75F and 50% RH. if you based it on 24/7 operation it is probably the same amount of moisture that a 25 pint a day dehu extracts.

I have not worried too much about the latent gains of occupants in a pressurized home in a while now. I just make sure I can cool off and dry the fresh air suffciently before it gets into the space.

[oldfella]

Thank you everyone, that's very helpful!

I realize now that SHR .5 is too much to ask, but thanks to this thread I have a realistic target to shoot for with the HVAC engineer and we will make up the difference with a dehumidifier.

The reason the SHR is so low is that we are factoring in some passive cooling - earth temperature stuff. This can manage all the cooling in fact, but none of the latent load. So we could get by with just a humidifier. I just thought "why waste free cooling?" If you have to run a dehumidifier in our climate, we would want cooling and not (re)heating.

Thanks again.

[Shophound]

Interesting article on Wiki re: passive earth tube cooling:

http://en.wikipedia.org/wiki/Ground-coupled_heat_exchanger

[teddy bear]

And I say tailor the ventilation strategy to the local climate and building type, use, and layout.

For humid regions, introducing untreated fresh air into the structure is counterproductive. Yes, we need to ventilate. That is not in dispute, nor should be by anyone concerned. The focus is on what is the best way for a given climate and structure. Ventilating dehumidifiers can be one way, so can a correctly balanced ERV. For my neck of the woods, fresh air intake on the a/c return can work, given our window of "cool, wet weather" is rather short.

And... I don't sell anything. I'm only interested in methods that work the best for a person's given budget and health/comfort needs, do not hazard the building, and do not waste energy needlessly.

And I say tailor the ventilation strategy to the home and the occupants. You need fresh air in the home to purge indoor pollutants and renew oxygen when the home is occupied. You need humidification when the home to dry and dehumidification when the home is to damp. No fresh air when the outside air is damp is not the most ideal for comfort and indoor air quality for an occupied home. If you figure out how to balance an ERV to provide indoor humidity control during wet cool weather, please sure the info. I tried to for several years and am still interested. I migrated to dehumidification over a 25 years while trying to provide ventilation systems for comfort and health. And yes, I turned out being a dehumidifier salesman. Looking forward to the education. Regards TB

[Carnak]

If you have to run a dehumidifier in our climate, we would want cooling and not (re)heating.

Thanks again.

A dehumidifier uses hot gas reheat

[beachtech]

That sounds like a dehumidifier salesman. That just wants to sell dehumidifiers to people weather they need one or not.

If he builds his house right. He won't have that high latent load he describes.
Unless he brings in more fresh air then he needs.

you got mail :)

[beenthere]

you got mail :)
Got it, thanks. :)

[Carnak]

Looking forward to the education. Regards TBI think you have been skipping school lately :) How about that North Carolina?

[oldfella]

Kinda out-of-the-box, but this company markets a DryMax mini-split pool dehumidifier. It cools,heats, or anything in between.
http://www.williamshvac.com/PDF/Dehumidification/drymax_product_access_cat.pdf

For the 2.5 ton, at 90F, 60% RH it claims an SHR of .49! It doesn't claim any numbers for the 1.5 ton unit which is too bad, since that's about the right size.

Thoughts?

[ascj]

What would be the best central heat pump for a very small load ( 2 tons ok, 1 ton would be best) very low SHR .5 (high latent load), and centrally distributed. Energy usage should be as low as practical.

We are building a super insulated passive house for mixed humid climate (Philadelphia). The high insulation and reduction of solar gain means that it has relatively little sensible load. It's a pretty big house and the floor plan is not open, so we are reluctant to use a mini-split unless we can connect it directly to the air distribution.

Anything come to mind? It seems hard to find SHR (sensible heat ratio) numbers on the web, is there a good source for this?

Thanks!

Have you looked at the Lennox Humiditrol system? You can get to .25 SHR on a 1.5 ton system.

[Carnak]

Kinda out-of-the-box, but this company markets a DryMax mini-split pool dehumidifier. It cools,heats, or anything in between.
http://www.williamshvac.com/PDF/Dehumidification/drymax_product_access_cat.pdf

For the 2.5 ton, at 90F, 60% RH it claims an SHR of .49! It doesn't claim any numbers for the 1.5 ton unit which is too bad, since that's about the right size.

Thoughts?So if you wanted to keep your place at 90F and 60% RH it has the SHR you are looking for. Probably any resi system would have an SHR of 0.5 if it was drawing in all outside air.

[oldfella]

Well that's good to know. I'd rather use something less esoteric.

PassivHaus systems have been traditionally 100% outside air. This is the best system I think. It's got a bit of a following in commercial hvac, but not for residential.

[beenthere]

Kinda out-of-the-box, but this company markets a DryMax mini-split pool dehumidifier. It cools,heats, or anything in between.


For the 2.5 ton, at 90F, 60% RH it claims an SHR of .49! It doesn't claim any numbers for the 1.5 ton unit which is too bad, since that's about the right size.

Thoughts?

At an indoor temp of 80°F and 51%RH, I can get a .60SHR out of a 13 SEER E1RD018(1.5 ton HP).

The drymax 2.5 ton at 82°F 50%RH is only .679SHR

So how hot are you keeping this place?

[oldfella]

Definitely on the cool side of 82, but I was thinking we could set it up to treat the incoming air. That will definitely be over 82/60rh or we probably won't have the system running.

PassivHaus was designed for the cooler/dryer climates of Germany but the PassivHaus HVAC concept was essentially conditioning 100% outside air, no recirculation. We hope to design something close to this, but we need something to handle the humidity waves we get periodically in Philly.

The humiditrol reheat coil also looks very interesting at 1.5 ton! I think this is my new favorite solution since I know we have multiple Lennox dealers in the area. Any negatives on this? It seems roughly comparable to the AAON system, we do have at least one AAON dealer too. Any strong feelings about Lenox vs AAON?

Sorry to be so dense on this. I really appreciate the help I'm getting here.

[beenthere]

If your mixing outdoor air and indoor air.

You have to design for the mixed ratio. Not one or the other.

[Carnak]

Well that's good to know. I'd rather use something less esoteric.

PassivHaus systems have been traditionally 100% outside air. This is the best system I think. It's got a bit of a following in commercial hvac, but not for residential.

your HVAC engineer should be able to find you a commercial grade dehumidifier, even one with a remote condenser that can function as both an air conditioner and a high powered dehumidifier at the same time.

He should also be able to find you a commercial grade humidifier, something like Dri-Steem for use in the winter

while you should get some sensible cooling and even a little mositure condensing in those earth tubes in the summer time, I think in the winter the air is going to be cool. Tough call but you are probably better off with a big ERV

[Shophound]

your HVAC engineer should be able to find you a commercial grade dehumidifier, even one with a remote condenser that can function as both an air conditioner and a high powered dehumidifier at the same time.

He should also be able to find you a commercial grade humidifier, something like Dri-Steem for use in the winter

while you should get some sensible cooling and even a little mositure condensing in those earth tubes in the summer time, I think in the winter the air is going to be cool. Tough call but you are probably better off with a big ERV

Unless I missed it, what this thread seems to be lacking so far is any design details...is the dehumidifier or the a/c supposed to draw 100% air from the earth tubes? Problem right off with a dehumidifier, unless I'm off track (not the least bit impossible :D) is the reheat factor. You're bringing air in through the earth tubes to take advantage of cooling outdoor air via the earth, yet since most earth coupled heat exchange systems aren't great dehumidifiers, you gotta then wring moisture out of the air during high outdoor dew point times. BUT...wringing moisture from the air requires energy, and with energy comes heat. THEN you'll need to remove that heat to keep from overheating the house, which is superinsulated and airtight.

Other thoughts...let's say Philly's summer design day is 91 dry bulb/74 wet bulb, rendering dew point at 67. Induct that air into an earth tube with wall surfaces below 67 degrees =100% saturation inside the pipe.

With straight a/c using earth tube for make-up air to purge indoor pollutants, what's better...sucking 100% saturated air mixed with the return air of the structure into the air handler, or using an ERV exchanging sensible and latent heat from structure with incoming air directly from outdoors?

[oldfella]

Here's my amateur look at this:

4000sf house + 2000sf basement. Philadelphia July has 363 cooling degree days, so by PassivHaus standards we only have about 3KW to spend on cooling.

Consider 100cfm ventilation + 20cfm infiltration.
1 pint/hour of internal water vapor
Inside it's 80F, 45rh
Outside it could be 100F, 100% rh
I calculate in this extreme we want to remove 13.7 pints per hour. Maybe the ERV knocks out 30% of that so we have 9.6 pints per hour.
Some high end dehumidifiers claim 6 pints/kw
So in theory we can do this, but I can't add 2KW of heat to the house like a conventional dehumidifier might do.

100% outside air is not a requirement, I just thought it might help the efficiency since you have most of the water vapor you want to remove in one place, and it wouldn't incur any extra energy cost to distribute the dry air. This is easy to do with heat, but I'm realizing this is probably a lot harder to do with refrigeration equipment which will be difficult to match to the load.

We are not really considering earth tubes, we have well water we can use for radiant cooling. We have other strategies like night time ventilation/radiant cooling and lots of extra mass. None of these strategies help with humidity. We will have the house stuffed full of cellulose (even interior walls) so this should help buffer the humidity.

[Shophound]

Here's my amateur look at this:

4000sf house + 2000sf basement. Philadelphia July has 363 cooling degree days, so by PassivHaus standards we only have about 3KW to spend on cooling.

Consider 100cfm ventilation + 20cfm infiltration.
1 pint/hour of internal water vapor
Inside it's 80F, 45rh
Outside it could be 100F, 100% rh
I calculate in this extreme we want to remove 13.7 pints per hour. Maybe the ERV knocks out 30% of that so we have 9.6 pints per hour.
Some high end dehumidifiers claim 6 pints/kw
So in theory we can do this, but I can't add 2KW of heat to the house like a conventional dehumidifier might do.

100% outside air is not a requirement, I just thought it might help the efficiency since you have most of the water vapor you want to remove in one place, and it wouldn't incur any extra energy cost to distribute the dry air. This is easy to do with heat, but I'm realizing this is probably a lot harder to do with refrigeration equipment which will be difficult to match to the load.

We are not really considering earth tubes, we have well water we can use for radiant cooling. We have other strategies like night time ventilation/radiant cooling and lots of extra mass. None of these strategies help with humidity. We will have the house stuffed full of cellulose (even interior walls) so this should help buffer the humidity.

100 degrees dry bulb at 100% relative humidity gives a dew point of 100 degrees and a wet bulb of 100 degrees. This is extremely unlikely for Pennsylvania, let alone even more hot, humid regions of the world. As it is, Philadelphia summer design conditions are 90 degrees dry bulb at 74 degrees wet bulb. Even Key West, Florida, at 90 degrees dry bulb, 78 degrees wet bulb, doesn't check in at 100/100.

[Carnak]

Unless I missed it, what this thread seems to be lacking so far is any design details...is the dehumidifier or the a/c supposed to draw 100% air from the earth tubes? Problem right off with a dehumidifier, unless I'm off track (not the least bit impossible :D) is the reheat factor. You're bringing air in through the earth tubes to take advantage of cooling outdoor air via the earth, yet since most earth coupled heat exchange systems aren't great dehumidifiers, you gotta then wring moisture out of the air during high outdoor dew point times. BUT...wringing moisture from the air requires energy, and with energy comes heat. THEN you'll need to remove that heat to keep from overheating the house, which is superinsulated and airtight.

Other thoughts...let's say Philly's summer design day is 91 dry bulb/74 wet bulb, rendering dew point at 67. Induct that air into an earth tube with wall surfaces below 67 degrees =100% saturation inside the pipe.

With straight a/c using earth tube for make-up air to purge indoor pollutants, what's better...sucking 100% saturated air mixed with the return air of the structure into the air handler, or using an ERV exchanging sensible and latent heat from structure with incoming air directly from outdoors?There is a lot of data missing, but like I said I am pretty skeptical of a 0.5 SHR. Look at it from the point of the AC or dehumidifer only drawing in room air. Means ventilation air goes right into room air and the house is a mixing box.
http://i32.photobucket.com/albums/d41/a_bee_normal/ADP.jpg

Every process line has the following in common. An SHR 0f 0.5 and a 20 degree temperature differential. One line is unique, there is actually an apparatus dew point possible, so this means that a cooling coil alone can supply air at the correct temperature and mositure content to maintain 80F and 70% RH. When there is no ADP possible it means that when you just use a cooling coil, you can have the air at the correct temperature just it is going to be too humid, or you can have the room air at the correct dewpoint its just that it is going to be really cold in there. You get in situations where you cannot have your cake and eat it too.

The other lines have no ADP possible, you cannot extend the process line to cut the saturation curve. This is telling you that to maintain the condition you have two choices 1) Over cool the air to get the mositure out and reheat it, or 2) Use a desiccant to literally suck the mositure out of the air.

Here is sort of looking at it with a 50/50 mix of room air and earth tube air going into the coil, treating the fresh air before it gets mixed into the space. Again you cannot get that mixed air cooled down at the rate of an SHR of 0.5. You have to over cool it and reheat it.

http://i32.photobucket.com/albums/d41/a_bee_normal/EarthTube.jpg

So like I said , I am pretty skeptical that there is a 0.5 SHR requirement in the first place. That is like a Pentacostal Church load

[Carnak]

If you went 100% outside air from an earth tube you would cool the earth tube air first down to about 55F and would be gold, just need to recirculate air in the winter

[oldfella]

Of course (slaps head vigorously), I need to earth cool it before it hits the desiccant wheel and coil. Big difference, especially at peak load. Thanks!

[Carnak]

Theoretically, if your earth system cooled the outside air to a damp 67F, you could get away with about 318 CFM a ton +/- and have no shortage of fresh air. Now in the winter that kind of volume of outside air is going to really be too dry, you would have to cut back from 100% mode so your lips would not split and just to avoid the energy of heating up all the cool air.

Now even if those tubes could drain, you are going to have a moist environment inside them in the summer and it is not impossible that there will be no shortage of pollen, insects, organic matter etc in those tubes and sort of self defeating the benefit of fresh air.

[Shophound]

There is a lot of data missing, but like I said I am pretty skeptical of a 0.5 SHR. Look at it from the point of the AC or dehumidifer only drawing in room air. Means ventilation air goes right into room air and the house is a mixing box.
http://i32.photobucket.com/albums/d41/a_bee_normal/ADP.jpg

Every process line has the following in common. An SHR 0f 0.5 and a 20 degree temperature differential. One line is unique, there is actually an apparatus dew point possible, so this means that a cooling coil alone can supply air at the correct temperature and mositure content to maintain 80F and 70% RH. When there is no ADP possible it means that when you just use a cooling coil, you can have the air at the correct temperature just it is going to be too humid, or you can have the room air at the correct dewpoint its just that it is going to be really cold in there. You get in situations where you cannot have your cake and eat it too.

The other lines have no ADP possible, you cannot extend the process line to cut the saturation curve. This is telling you that to maintain the condition you have two choices 1) Over cool the air to get the mositure out and reheat it, or 2) Use a desiccant to literally suck the mositure out of the air.

Here is sort of looking at it with a 50/50 mix of room air and earth tube air going into the coil, treating the fresh air before it gets mixed into the space. Again you cannot get that mixed air cooled down at the rate of an SHR of 0.5. You have to over cool it and reheat it.

http://i32.photobucket.com/albums/d41/a_bee_normal/EarthTube.jpg

So like I said , I am pretty skeptical that there is a 0.5 SHR requirement in the first place. That is like a Pentacostal Church load

Great post, especially that last chart. Took a bit to get my head around it, but once it latched on and the light went on...ha!

Laying your second chart info out on my own psych chart, I'm coming up with a SHR of around .53 for the mixed air process line and around .73 for the process line from ADP to entering room air condition @ 80/45. So...if the 91db/74wb enters the earth tube and goes to saturation within the tube, going by the chart it appears air entering the return air path from the tube would be 67 degrees at 100% saturation, and air from the room is 80 degress at 45% saturation, resulting in a mixed air state of 73.5 @ 68% RH (62 degree dew point) going into the cooling coil.

Am I on the right track, here?

[oldfella]

Understood about the problems of earth tubes. Our current thinking is heat exchange by pumping water in closed loop or take advantage of existing wells (open loop) to achieve earth cooling, like Zehnder ComfoFond-L system.

[Carnak]

Laying your second chart info out on my own psych chart, I'm coming up with a SHR of around .53 for the mixed air process line and around .73 for the process line from ADP to entering room air condition @ 80/45. So...if the 91db/74wb enters the earth tube and goes to saturation within the tube, going by the chart it appears air entering the return air path from the tube would be 67 degrees at 100% saturation, and air from the room is 80 degress at 45% saturation, resulting in a mixed air state of 73.5 @ 68% RH (62 degree dew point) going into the cooling coil.

Am I on the right track, here?

thanks

I was just showing that you could not find a coil that would cool the mixed air at a 'rate' of SHR = 0.5. You would have to over cool it to get the same dewpoint as you needed for the impossible process and then reheat it. You over cool the mixed air down to the dewpoint you need then reheat it so the process keeps running. Two steps needed to get the leaving air condition associated with SHR=0.5.

The first chart shows that the only way a coil only could give you an SHR of 0.5 is if the space (or the air entering the coil) was pretty humid to begin with.

Sort of also makes a case for treating the outside air first as opposed to trying to 'squeeze blood from a stone' and super dehumidify air that is already dry in order to compensate for untreated humid air being added to the space either deliberately by ventilation or unintentionally through infiltration.

Now concerning SHR, there is what the room needs 'based on sensible and latent gains in the room, and there is an SHR that the coil sees, and quite often this is where the ventilation load is dealt with.

In my second chart, the SHR of 0.5 (on a coil) is not possible, so the SHR used is from the mixed air to the 49.4 air, it looks steeper than 0.73. I think 0.73 is you looking at the room condition 80F and 45% and the 49.4 fog coming off the coil.

Can't really say what the load of the room is as the OP was never clear on it.

[oldfella]

So I was thinking (always dangerous) - I don't need to run this continuously. I can run this 20 minutes every hour, drag my earth cooled/wet air through a 1 ton AC Coil, and stay cool, dry, ventilated, and certified under my energy budget. Thanks again everyone.

Revisiting the original question, 1 ton is still pretty small, does this suggest any particular pieces of equipment? Probably a ducted mini-split comparable to Daikin or mr slim? Anything made in the US? Anything made near Pennsylvania?

[Carnak]

Understood about the problems of earth tubes. Our current thinking is heat exchange by pumping water in closed loop or take advantage of existing wells (open loop) to achieve earth cooling, like Zehnder ComfoFond-L system.

Well a water coil if it got your fresh air down to the mid 60s, probably not a real big energy penalty going 100% outside air. Pre-cool all the fresh air down with the water coil then cool it with a normal system to dehumidify it.

Even with it cycling infrequently, that would be a big shot of fresh air every time. 12 minutes of 800 CFM fresh air is like two hours of 80 CFM steady.

[Carnak]

So I was thinking (always dangerous) - I don't need to run this continuously. I can run this 20 minutes every hour, drag my earth cooled/wet air through a 1 ton AC Coil, and stay cool, dry, ventilated, and certified under my energy budget. Thanks again everyone.

Revisiting the original question, 1 ton is still pretty small, does this suggest any particular pieces of equipment? Probably a ducted mini-split comparable to Daikin or mr slim? Anything made in the US? Anything made near Pennsylvania?

Put in a 2 ton system, run it down around 320 CFM a ton then. 640 CFM every time it kicks on is a lot of fresh air. Try you have plenty of fresh air if it ran 10 minutes an hour.

[oldfella]

Yea, the reason I wasn't clear on the room load is that we are kinda working backwards into that. PassivHaus certification is like the NFL salary cap, it's all about staying under your energy budget. Windows are the real budget busters for cooling; one part of the exercise is to see how many windows we can afford and still get certified. Thanks to you guys we might get a couple more windows.

[ACFIXR]

Look at your duct location, it is possible to get the gain to zero.

[Carnak]

Great post, especially that last chart. Took a bit to get my head around it, but once it latched on and the light went on...ha!

Laying your second chart info out on my own psych chart, I'm coming up with a SHR of around .53 for the mixed air process line and around .73 for the process line from ADP to entering room air condition @ 80/45. So...if the 91db/74wb enters the earth tube and goes to saturation within the tube, going by the chart it appears air entering the return air path from the tube would be 67 degrees at 100% saturation, and air from the room is 80 degress at 45% saturation, resulting in a mixed air state of 73.5 @ 68% RH (62 degree dew point) going into the cooling coil.

Am I on the right track, here?

Should have said yes, in the second chart outside air is going through the tube and getting cooled off to 67 almost saturated.I started at 91/74 as I think that is what you dug up.

Then "I mixed" the pre-cooled fresh air with an equal amount of room air and the OP was saying something like keeping his place hopefully at 80F and 45%.

So I was just doing screen shots from an old windows 3.1 program but yes the mixed air is somewhere around 73.5 and 68% like you were saying. Then I drew a line with a slope of about SHR of 0.5 down to where the air being cooled off was now 20 degrees cooler at 53.5. You cannot extend that line to the ADP so it is a big warning that you need reheat. Another sign of needing reheat is the required dry bulb and wet bulb numbers are not close together within a degree because normally when you are pulling a lot of mositure out of air it starts getting close to being saturated.

So then I looked at what the dewpoint of the air 53.5/51.1 was and it was actually something around 48.4. So then I just showed that you would have to cool that mixed air down to 48.4 then reheat it back up to 53.5 to get the same effect as a coil with a 0.5 sensible heat ratio.

Now if his earth cooling system could somehow precool that outside air down into the mid 60s it will have a similar heat content to room air at 75F and 60%. Even just pre-cooling it to 67 it has the same enthalpy as the 80/67 air they rate the systems at, however because it has high RH, it would be a no brainer that even standrard cooling equipment would pull a ton of mositure out of it.

So that is why I am saying if he can pre-cool the air outside air enough now apparently by just running a pump, there is no real energy penalty for going 100% outside air

[Carnak]

So I was thinking (always dangerous) - I don't need to run this continuously. I can run this 20 minutes every hour, drag my earth cooled/wet air through a 1 ton AC Coil, and stay cool, dry, ventilated, and certified under my energy budget. Thanks again everyone.

Revisiting the original question, 1 ton is still pretty small, does this suggest any particular pieces of equipment? Probably a ducted mini-split comparable to Daikin or mr slim? Anything made in the US? Anything made near Pennsylvania?

Your 1 ton coil is going to handle say 320 CFM without driving up RH.

So that air is coming out at 55F

If you keep it 80F in there, that means the system will give you 320 x 1.09 x (80-55)= 8720 Btu per hour of temperature control. So I would not be in a big hurry to be adding more glass. You want it cooler you have less temperature control trying to keep 75 F you only have about 7000 Btu available. Move more than 320 CFM through that coil and your indoor RH is going up you will need a dehumidifier. Nit pickers can note, typically when you base the calculation on cold supply air the sensible heat constant is 1.1.

A big well insulated house like that is going to hold on to its heat when the sun sets. Just due to its size, you are going to have a few watts of lighting turned on in there, your fridge cycles on and off and those big screen yuppie tv`s toss a few watts out also. Probably no shortage of computers or smart house controller stuff running in there also.

Residential calculations ignore lighting, anything other than basic appliances, thermal mass etc. The latest `manual j`is pretty skinny on the heat gain from glass if you ask me. Seems to be too scared people will over size.

So be prepared for warmer temperatures if on paper you still think a single ton is going to work. I did a 4000 square foot superinsulated place, R40 walls R60 ceiling, tested sealed vapour barrier, triple glazed, low e argon windows, in a northern location, and I still needed more than 8700 btu per hr sensible cooling. Heated the place with a 75K rheem drum against 100F differentials, could of went with a 2 ton AC I suppose, had a 2.5 ton. Competition was quoting twice the size of heating and cooling, basically the largest residential units he could get.

[oldfella]

A big well insulated house like that is going to hold on to its heat when the sun sets.

We are planning on doing night time ventilation based on the outside temperature and humidity, along the lines of the Arzel CoolMizer. Another approach that seems interesting is using solar water collectors in reverse at night to radiate heat into the atmosphere. This would be complicated to set up, but would work on days where it remained humid all night. We will also have available earth cooling directly to the house in radiant panels or fan coil.



So be prepared for warmer temperatures if on paper you still think a single ton is going to work.

I do want to be prepared for occasional high loads, What about a 1 ton/2.5 ton two stage compressor? Does such a beast exist? It could run half the time in ventilation/dehumid mode, and the other half time it would be available to answer zoned cooling calls. With a big enough 2nd stage I should have my bases covered without increasing my baseline energy usage. Wouldn't a 1 ton/? ton two stage compressor generally be as good for dehumidification as a 1 ton single stage compressor? I don't want to handicap my 95% case to handle the 5% case, but I also don't want to sweat buckets 5% of the time.

[oldfella]

Would it be crazy to use a reverse cycle chiller for this application?

The smallest ones are 3 ton, but a storage tank could potentially buffer the chilled water so I could use as little as needed without short cycling.

[beenthere]

Sounds like over kill.

But should work.

[teddy bear]

Earth tubes in green grass climates have big mold problems during high outdoor dew points. The tubes have wet surfaces with dust/mold spore that grow mold. I suggest that you have a large dehumidifier ready to dryout your home after a night of summer ventilation +65^F dew point air. The materials in the home will absorb enough moisture providing enough moisture for dust mites in upholstured materials and mold growth on the cool surfaces. Dampness for more than 48 hours grows mold. A throurgh drying every day is good. Damp evenings preceded and followed by several rainy days could make a mess out of a nice home. Maybe a small a/c with a good erv/dehumidifier is a better(safer) option. Being uncomfortable and having a musty odor with a nice home is not ideal.
Regards TB

[oldfella]

We are not using earth tubes, problems noted though, as you said by many observers. I agree night ventilation is not practical unless it is tied to enthalpy of the outside air. The night ventilation mode won't even turn on if the outside air carries more water vapor than the inside air.

My issue with dehumidifiers is the heat added to the air. Usually I don't want it, and I will just need to burn a/c cycles to get rid of it.

[teddy bear]

We are not using earth tubes, problems noted though, as you said by many observers. I agree night ventilation is not practical unless it is tied to enthalpy of the outside air. The night ventilation mode won't even turn on if the outside air carries more water vapor than the inside air.

My issue with dehumidifiers is the heat added to the air. Usually I don't want it, and I will just need to burn a/c cycles to get rid of it.
If you have cooling load, the a/c will control the humidity. Therefore the dehumidifier will only operate when the a/c is not able to maintain <50%RH or setting. This is not a conflict. The dehu wins two ways. The dehu reduces the moisture and raises the temperature which also lowers the %RH. 1^F rise in temp is a 2%RH reduction. I do both minimal cooling with dehumidification. Both never run together. Controls are avialable to make sure. After cooling is finished, the dehu will reduce moisture to setting. If that was enough to raise the temperature above the t-stat, the a/c will cool and remove more moisture. Regardless keep a good dehu is reserve to maintain low %RH. Regards TB