To chill or Not to Chill, That is my question

Housedoc

GREETINGS,

I am working on a 6000 sq. ft home with a heated and cooled garage. There is also a detached 2-car garage and a pool kitchen/dressing-bathroom to be heated and cooled. We are installing radiant in the house using a water to water ground source heat pump (GSHP) and 1-1/2" lightweight concrete over floor loops. But, I am undecided on the cooling/dehumidification system and value opinions. Do you favor:



(1) Water to water GSHP's for radiant heating with separate conventional GSHP's using Dx coils for cooling and dehumidification using forced air.



OR



(2) Reversible water to water GSHP for radiant heating and chilled water with four pipe air handlers for cooling and dehumidification using forced air.



Although Option #2 gives me a bit more flexibility, I cannot help but think there is an energy penalty as we are moving heat from (a) the earth to the refrigerant, (b) from the refrigerant to the chilled water, (c) from the chilled water to the air. With Dx, we are moving heat from (a) the earth to the refrigerant and (b) from the refrigerant directly into the air.



We would set up two buffer tanks (hot and cold) and run heated and chilled water to each air handler so we can remove humidity and provide reheat.



Any thoughts?

Mark Eatherton

You forgot one potential option...

Radiant cooling. Here is a link to Robert Beans web site, healthyheaitng.com that pertains to radiant cooling. Same principles as radiant heating, only cooling.



http://www.healthyheating.com/Page%2055/Page_55_i_cooling_eq.htm#.UCEbM0JNzGk



At least worth consideration, and could reduce your installed costs and deliver more efficient comfort.



ME

Housedoc

Radiant cooling

Would love to try it Mark. But I am in a mixed humid climate called the rot belt. Moreover, I didn't want to use homeowner as a guinea pig ----even with Robert's encouragement.

Mark Eatherton

Then consider chilled beams...

http://air-commodities.com/PDFs/Chilled_Beam_Design_Guide-TB020209.pdf



It is designed to control humidity. And provide quiet cool comfort.



Gotta think outside the box some time ;-)



"If you keep doing what you've always done, you'll keep getting what you always got" author unknown...



I'm doing a radiant ceiling cooling system at my mountain home using Mother Earth as the coolth source. But I don't have ANY condensation issue potentials at all, except when it is thundering and raining outside, when I wouldn't need cooling anyway. I understand your fears.



ME

NRT_Rob

I like chilled water

but some thoughts.



1. pipes must be very well insulated. I am considering using insulated linesets as refrigeration does, honestly. insulation quality otherwise appears to be... spotty... as heating guys just don't usually have to worry about insulation like you do for chilled water apps.



2. chilled water air handlers do not have to worry about minimum airspeeds. so you can zone with impunity and run static pressure controls on ECM fans to really crank back fan power usage. this is also awesome for dehumidification control... could probably go back to two-pipe/no reheat if you run aggressively modulated equipment. and if you don't need simultaneous heat/cool, you could probably drop the second buffer tank.



3. chilled water will technically be less efficient, as you note, not just for the multiple exchanges but also because you are exchanging into cold water instead of room temperature air. but with zoning efficiency gains, and fan power improvements, I doubt the difference will mean much. And you have to look at the cost of the additional DX equipment and figure out how long any efficiency gain would really take to pay back that equipment. I suspect the answer is "a very long time". Further, you should be able to nail comfort better with the chilled water system.

Housedoc

Great Comments

Excellent feedback. I would love to tackle the radiant cooling. But the house must have dehumidification and ventilation air. So I am still stuck with installing ducts.



Dehumidification choices would be a Dx type system as with the Thermastor Products. Or, going back to chilled water air handlers and using heating coil for reheat. At the end of the day, how much benefit have I provided the owner versus using Dx coiling with hot gas reheat for dehumidification?

NRT_Rob

I'm not sure

you need reheat if you're using chilled water air handlers. If you need less cooling you can slow the fan down.



here at our shop, for example, we run a chilled water coil in our ERV ductwork. we maintain 45% RH without overcooling because it's a very, very low airflow.

Housedoc

Me Neither

I am not sure if reheat would be required either. But my experience with Dx cooling and dehumidification would say it would be necessary.



A few years back Carrier came up with the idea to incorporate a humidity sensor in their thermostat. The homeowner would set the desired temp and the desired RH. When the RH rose above the set point, the AC would energize and the blower would slow to produce a much colder evaporator coil. The unit usually did a good job removing more humidity. But the room temp begins to drop. When the room temp dropped, the RH went up. So Carrier came back and adjusted the firmware to not allow the room temperature to drop more than 3 to 5 degrees below the thermostat set point. They called this droop.



Since then Honeywell as replicated the idea. But in all cases, a well insulated, substantially airtight home would fall below a comfortable temp when the unit was trying to reach humidity set point. That's why I have found it necessary to install reheat.



With ground source heat pumps using dx cooling, I can specify hot gas reheat, which recirculates refrigerant hot gas off the compressor through a reheat coil to prevent over cooling. I have also used a hydronic coil being heated with solar hot water and heated water from triple function ground source.



We have many days in the spring and fall with outdoor temperatures of 72 to 74 degrees and the ac simply aint coming on. Ventilation air and natural infiltration begin to elevate the indoor moisture levels. Without AC running, we have to have some type of dehumidification.



After 35 years or so in dealing with homeowners, I am really paranoid of not recommending tried and proven technology. I am just afraid not to do reheat. And if I need ducts for ventilation, dehumidification and heating coils for reheat, I am still uncertain about the benefit of using radiant cooling.

Housedoc

Me Neither

I am not sure if reheat would be required either. But my experience with Dx cooling and dehumidification would say it would be necessary.



A few years back Carrier came up with the idea to incorporate a humidity sensor in their thermostat. The homeowner would set the desired temp and the desired RH. When the RH rose above the set point, the AC would energize and the blower would slow to produce a much colder evaporator coil. The unit usually did a good job removing more humidity. But the room temp begins to drop. When the room temp dropped, the RH went up. So Carrier came back and adjusted the firmware to not allow the room temperature to drop more than 3 to 5 degrees below the thermostat set point. They called this droop.



Since then Honeywell as replicated the idea. But in all cases, a well insulated, substantially airtight home would fall below a comfortable temp when the unit was trying to reach humidity set point. That's why I have found it necessary to install reheat.



With ground source heat pumps using dx cooling, I can specify hot gas reheat, which recirculates refrigerant hot gas off the compressor through a reheat coil to prevent over cooling. I have also used a hydronic coil being heated with solar hot water and heated water from triple function ground source.



We have many days in the spring and fall with outdoor temperatures of 72 to 74 degrees and the ac simply aint coming on. Ventilation air and natural infiltration begin to elevate the indoor moisture levels. Without AC running, we have to have some type of dehumidification.



After 35 years or so in dealing with homeowners, I am really paranoid of not recommending tried and proven technology. I am just afraid not to do reheat. And if I need ducts for ventilation, dehumidification and heating coils for reheat, I am still uncertain about the benefit of using radiant cooling.

NRT_Rob

yes

with DX, that's all true. the minimum airspeed you need to make the compressor happy will cool the building.



with water, you can buffer in the water stream. there are NO minimum airspeeds to consider. there are some situations where internal humidity gains may be very high and it is cool out but in general, you can just slow the fan speed far below any DX fan speed level and shift your cooling ratio further and further to the 'latent' side.



even at 200 CFM, our ERV will only generate 4kBTU of cooling for a 3500 sq ft building. and it typically runs at about 75. pretty hard to overcool with that. dehumidifies nicely though.

JB40

Chilled Water Hands Down

Wow, what a project. As I read through this thread I couldn't help but wonder who's going to maintain this system?  Amazing design concepts using all the latest technologies, but I'd be concerned it will require a part time service tech. to keep all the controls communicating properly.  I'd go chilled water for the same simple reasons mentioned already:

1) Centralize the AHU to limit the number of individual terminal units the end user needs to maintain.

2) VFD on the AHU fan motor to reduce sound and energy usage.

3) VAV's with HW reheats serving each space.

Your higher water temps will probably require slightly oversized chilled water coils, not always easy to find in off-the-shelf fan coil units, but probably easy enough to retrofit: http://www.h-mac.com/hvac-coils/chilled-water-coils.html

Housedoc

To reheat or not to reheat. That is my question now.

Rob brought up some interesting thoughts about dehumidification. It appears that using chilled water is extremely more flexible than Dx. With Dx, there is always s danger of freezing a coil when airflow is reduced too much. But that is not as big of a concern with chilled water. I am not sure I have the physics in my head like Dx. With Dx, reducing airflow means a colder coil, which enhances dehumidification. But with chilled water, lower airflow does produce a colder coil or at least no colder than the EWT. At any rate, could reducing airflow with chilled water possibly eliminate the need for reheat?

Bob Gagnon plumbing and heating

Radiant Cooling

I installed this simple system in my house 12 years ago, its on right now. Cold water simply circulates first through a fan coil unit, removing humidity, cooling and moving the air, then the slightly warmer water circulates through the radiant system. No condensate issues and unbelievable comfort. There has been no maintenance issues with the simply system, it seems like the way to go.



Thanks, Bob Gagnon

SWEI

nice

I've been looking at direct exchange with groundwater for a couple years now, but have yet to build one.  I assume there's no need for sprinklers in the heating season, since it looks like hot water circulates through the same HX?

JStar

Chilled ceilings

I am in the middle of designing a chilled ceiling system for a customer. Following this thread like a hawk. I see a lot of great comments here, and hope to contribute my own.



Radiant ceilings with a chilled coil dehumidifier seems like the way to go. I was planning to incorporate a reheat coil off the compressor discharge. What is the practical length of a discharge line?

JStar

Tubing

Is there any chart for the cooling ratings of PEX at different spacings? It seems that all chilled panels are 6" on center. I have a few rooms that require more BTUH per square foot than that can offer. The calculations make me believe that 3 or 4" on center will be needed in some areas. Will tighter grouping make a difference?

Bob Gagnon plumbing and heating

Heating Season

The boiler water still circulates through the flat plate exchanger in the winter, but since the boiler is running and the sprinkler pump is not the radiant would be heated,not cooled.



Thanks, Bob Gagnon

Bob Gagnon plumbing and heating

Chilled Ceilings

I have chilled ceilings and some walls have radiant too, my mattress also. A fan coil unit will provide dehumidification and will also provide a substantial part of the cooling, I think almost half in my house.



Thanks, Bob Gagnon

JStar

Cool

That's awesome! Always a cold side of the pillow in the summer.



My particular customer does NOT want to have any noticeble airflow or registers in the house. I'm extremely close to being able to satisfy the entire sensible load with chilled radiant. The latent load is only 3,243 BTUH. I can satisfy the latent load with 40F water at 320 CFM. Spread that over 17 rooms, and the airflow should be a whisper. That also lets me use the chiller for humidity control, saving a whole extra system.

NRT_Rob

in general

if you need much more than 20 BTU/sq ft of cooling from a ceiling, you need supplemental. That's a physical limitation in most cases unless you are in a super arid climate.



might need to add some wall if you can't do air backup.

JStar

Walls

I can make the numbers work if I add wall coverage. The customer also has radiant floors that I may need to use for cooling as well. Floor output is only about half of what the ceiling is, though. I'm just worried about having too much tubing in the walls where they are susceptible to nails and screws. I'll be safe if I don't completely secure the tubing in the wall bays? Give them some room to move around?

NRT_Rob

we have

floor and ceiling and I have to say, it doesn't seem to impact output much. probably because the floor is purely a radiant addition and it's facing an already cold surface, the ceiling. Walls would probably be better because they are perpendicular to the ceiling.



ALL TUBING will need plates if you're doing drywall. you want as close to complete aluminum coverage as possible. walls or ceiling. no loose pipe.

JStar

Walls

Yeah, that was my concern. I was planning on plating all of the tubing. I guess I'll have to make sure that all of the circuits are high or low enough not to be in the picture-hanging range.



What do you suggest for partition walls that may need wall coverage in both rooms? Do you insulate between the two loops? Should I be insulating inside walls where only one room needs wall coverage and not the adjacent?

NRT_Rob

always

insulate the back side of a radiant panel, no matter what. otherwise you have an uncontrolled emitter. hard to get desired comfort that way.

JStar

Figured.

Thanks for the help.

SWEI

walls

We have installed plates using both horizontal and vertical orientations.  With metal studs, horizontal can work out better but it takes some work.  We notch the studs, use mostly 8' plates, and pop rivet them to the studs.  Once the tubing and plates are installed and pressurized we have the insulators blow the cavities.