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Hydronic Cooling in AZ

adamflyer's picture

I am in the process of designing a 1.5 story U-shape house with 3,600 ft^2 on the ground floor. The main section of the house is a rectangle, it will have an 8/12 TJI framed roof with load bearing ridge beam having and has a center section containing a large open room with vaulted ceiling for the living room, kitchen, and dining area with a ~500f^2 loft projecting into part of it. One end has the bedrooms and the other a garage, these ends will have insulated attic space above them that I will likely leave unfinished which can be later finished for use as a bonus room or storage.

The house will be built in Dewey, AZ. I have designed a double 2x4 exterior walls 24” oc 10” thick with blown in cellulose should yield ~ R-30 and 14” TJI rafters and 11-7/8” TJI floor will give enough space for R-38 or more fiberglass batts. I plan on sealing up the house as airtight as practical. The house is designed to get part of its heating load from its passive solar design https://www.youtube.com/watch?v=fNt-D_1CvAw. I have pretty well decided I want to go with hydronic system with an air-water heat pump of some sort for heating and cooling because I would like to be able to shift the cooling load to off peak electric rates with heat storage tanks. I am undecided about using air handlers or radiant panels for distributing heating/cooling loads in the house. My biggest beef with traditional HVAC is running poorly insulated duct work in unconditioned space. I do have space in the attic (which is in insulated space) for running central air ducts if needed. That being said, independent ductless air handlers or a radiant system would be preferred for its zoning capability.

I have checked out some options of radiant ceilings with pex tubing behind the drywall. I have an engineering background and am not intimidated by control systems but I am nervous about a system failure in monitoring the dew point and getting moisture behind drywall due to condensation or a leak. My last idea I have is to do a dropped ceiling with 2x2 ceiling tiles but use radiant panels for heating/cooling. I think done with the right kind of trim on the grid it could look nice and not have the industrial office building look.

Some questions.

  1. Is blown in cellulose in a double wall going to be an issue in my climate and should I consider other insulation materials?

  2. Can I seal up the airspace in my rafters or does it need to be vented?

  3. If I use purely radiant heating/cooling with no air handlers will an HRV ducted to one central location in the house be sufficient or will I need to provide ventilation to several rooms in the house

  4. Is it feasible to do radiant only cooling without an air handler or any means of controlling humidity for my climate?

  5. Does anyone know of any US suppliers of radiant ceiling panels for dropped ceilings (or anything where the panel is not behind drywall? Closest I found is in Canada.

Any other feedback welcome.

Thanks,

-Adam

1.  I don't see any issue (post #214940, reply #1 of 5)

1.  I don't see any issue with  using blown in celulose.  Go with what is best value for cost / effective R value.

2.  My preference is to an air gap under the roof deck, and have continuous ventilation at the soffits and ridge.  This gives some cooling of the roof deck, and reduce the heat load being conducted into the attic insulation.  Other will have different opinions.  Both methods can be made to work with some attention to detail.  What type of roofing will also affect the decision.  Asphalt shingles like to be cool.  Metal, clay / concrete  do not care.

3.  HRV should be ducted to extract air from the kitchen and baths, and supply air to the living areas and bedrooms.  Flow rates are low, small diameter pipes will be sufficient.  Easy to route through structure.

4.  You can run the radiant heating / cooling loops thought a slab  floor.  In cold climates, the slab should be insulated from ground with XPS foam boards.  Not sure if it will make a difference where you are.  Heat / cooling loss calculations will give you the answer to that.    Radiant cooling does not dehumidify, since the surface temperatures of the radiant panels / floor are only a degree or two lower than the desired room temperature.  You may need some supplementary dehumidification to take care of those rare days when it is both hot and humid.   Any dehumidifier can be ducted through the HRV system.

5.  Forget the ceiling panels.  Put the loops into the floor.

Go here :   http://www.healthyheating.com/Page%2055/... for more information on radiant heating / cooling and humidy control options.  

Cheers

Having the cooling loops only (post #214940, reply #2 of 5)

Having the cooling loops only in the floor won't work unless there is some scheme to blow air across the floor and up into the room.   You'll merely manage to create cold feet.


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

Radiant cooling does not (post #214940, reply #4 of 5)

Radiant cooling does not require convection to provide cooling.  It works by absorbing the heat radiation from the occupants or other warm objects in the room.  There is no requirement for any induced air movement, but a simple low speed ceiling fan, or the flow from the air exchange system (HRV) will minimize any air stratification.  For a well sealed house, the air exchange ventilation system will provide all the air movement necessary.

Using the floor provides a large surface area, for both heating and cooling.  The temperature of the floor will be only a few degrees cooler than the air. The same will be true if you use the ceiling for the radiant panel. 

The advantage to using the floor is the thermal mass of a slab, stabilzing the room temperature, and smoothing out the day / night  requirements.  It is also much easier to install, and usually less expensive than a ceiling installation. 

Advantages to using the ceiling as the radiant panel are it will induce a convective flow of air, and usually provides a more open space.  Problems are the expense of separate radiant panels, or if using the drywall as a panel, the installation of the cooling loops.

RE: I don't see any issue (post #214940, reply #3 of 5)

catmandeux wrote:

1.  I don't see any issue with  using blown in celulose.  Go with what is best value for cost / effective R value.

2.  My preference is to an air gap under the roof deck, and have continuous ventilation at the soffits and ridge.  This gives some cooling of the roof deck, and reduce the heat load being conducted into the attic insulation.  Other will have different opinions.  Both methods can be made to work with some attention to detail.  What type of roofing will also affect the decision.  Asphalt shingles like to be cool.  Metal, clay / concrete  do not care.

3.  HRV should be ducted to extract air from the kitchen and baths, and supply air to the living areas and bedrooms.  Flow rates are low, small diameter pipes will be sufficient.  Easy to route through structure.

4.  You can run the radiant heating / cooling loops thought a slab  floor.  In cold climates, the slab should be insulated from ground with XPS foam boards.  Not sure if it will make a difference where you are.  Heat / cooling loss calculations will give you the answer to that.    Radiant cooling does not dehumidify, since the surface temperatures of the radiant panels / floor are only a degree or two lower than the desired room temperature.  You may need some supplementary dehumidification to take care of those rare days when it is both hot and humid.   Any dehumidifier can be ducted through the HRV system.

5.  Forget the ceiling panels.  Put the loops into the floor.

Go here :   http://www.healthyheating.com/Page%2055/... for more information on radiant heating / cooling and humidy control options.  

Cheers

Thanks for the feedback

2.    I'm planning on a metal roof and either something close to white or the galvanized silver so as to limit the heat in the summer. When you say airgap under the roof deck you mean just not shoving insulation all the way up to the sheathing? If building a rafter roof with the insulation between the rafters with the venting this way how do you keep the house "air tight"? Does you drywall ceiling become an air barrier? I am looking at doing a pine or cedar plank celing on this one.

3.    Sounds like a good way of doing it.

5.    I'm going with a TJI floor. All the houses I have seen in the area are with slabs are very cracked due to the clay soil so its not something I want to deal with. At this point knowing ducting should be in order for every room I'm thinking of a central hydronic air handeler.

-Adam

2.  Leave a 2" gap between (post #214940, reply #5 of 5)

2.  Leave a 2" gap between the top of the insuallation and the bottom of the roof deck, vented at both the soffit and ridge. Unless you are using foam. the insuallation does not provide any air sealing in a roof.  The drywall, along with appropriate caulking,  will be the air seal.   For a plank ceiling, an air barrier can be installed to the joists, and then the planks.

4.  If the slabs are cracking that badly, someone is not doing their job properly. 

You can install heating / cooling loops in framed floors, just a little more work and expense compared to slabs.  Also, as a low mass system,  it becomes easier to adjust temperature quickly, but you loose some themal mass to smooth out heating / cooling loads.

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