Radiant Heat in Central/South Texas??

Mark Galbreath

All,

I am preparing to build a house in College Station, Texas, within the next year or so.

I started out thinking I wanted to add a electric radiant floor to the master bath to keep the floor comfortable. That idea has caused me to investigate heating my entire home with radiant heat (too some extent, see below). My wife and I don't like to be cold much, and we really like the idea of the warmth that radiant floor have to offer.

I would like to use a ground source heat pump to generate heat for the floors (and cool the house in the summer). The house will be pretty large (3800 sq ft on a slab, and another 400ish above the garage). I will use insulated concrete forms on the walls, and the attic will be sealed with icynene foam (so the attic air will be heated/cooled space). I will have an air exchanger that will run periodically to vent the house. This is a fairly new design idea down here. So, the house will be pretty well insulated and very, very tight. Humidity control in the summer is the goal.

As you can imagine, our temperatures are not really cold by northern standards here, as low as the teens but not usually for very long, and the next day the temperature outside my be in the 50's. My concern is that by using hydronic heat in the slab, I risk having too much latent heat built into the slab, and if the outside temperature swings too far upwards, the heat will run us out of the house. The slab will be pretty huge, and will be very thick.

Here is my idea for a solution that would enable me to take the most advantage of radiant heat....

Instead of using a thermostat to monitor the air temperature of the rooms, I would like to use a thermostat to control the slab temperature, and keep the slab warm, rather than hot (ok, a few degrees warmer in the bathrooms). I would cap the heat output of the floor this way by setting the floor temp to something pretty close to room temperature (I am making up a number here, of say, 75 deg F). If a particular room or zone needs further heat, the regular thermostat for that zone would call for heat from the air handler portion of the heat pump, and would be provided a boost for that room or zone.

I am focused on the Synergy system that is made by Water Furnace International for this purpose. I would like to use drilled holes on my 1.6 acre lot for the loops (maybe we will strike oil!!). The Synergy System will supposedly handle the production of hot water for heating, as well as domestic use. I do not have access to natural gas, so propane would be my only viable source of a bio fuel.

I would also like to insulate under the slab around the perimeter, say 8 feet or so. I feel if I overinsulate the slab, especially in the middle, I risk increasing my summer cooling requirement by not taking advantage of the relatively cool ground.

I am totally sold on the insulated concrete and icynene sealed attic.

I need you all to tell me if I am crazy on the hydronic floor... Especially if using a warm floor rather than a hotter floor will work in conjunction with forced air in zones.

Any suggestions or comments are welcome.

Thanks for your inputs...

Mark Galbreath

Mark Galbreath

I forgot to ask...

I forgot to ask...

If I do use water to heat the slab, I am a big confuzed as to some different types.

Some designs show a seperate pump for each zone of heating, and some show a manifold with mixing valves or temperature control valves attached, using just one pump for circulation. How do these systems differ?

What about a supplemental heat supply? Should I plan on adding a propane or electric water heater as a "storage tank" that will double as a supplemental heat supply for the system??

Can I simply monitor the temperature of the return line to control the slab temperature for that zone, or does a sensor in the concrete of each zone need to be placed and monitored.

I will be using a lot of travertine marble for the floors, but there will also be some carpet and some hardwood. In the case of the hardwood, it will be glued down to the slab. In all cases, will I need to add any kind of vapor barrier (as a result of the radiant heat) on top of the slab?? If so, how exactly will that work with the different materials...tile, marble, wood, and carpet?

Trust me when I say that I am forging into new territory down this far south...

Thanks again,
Mark Galbreath

hr

Not a bad plan

First off have a heat loss calc and design done for your home. I'd guess you see some very small heating loads with that construction.

The design will show you what water temperatures are needed for each room or zone. With hard surfaces I imagine temperatures will be very low. As such I would not worry about to much slab over shoot. Use a outdoor reset to limit extreme temperatures in the slab.

Better yet would be a dry "on top" system that would take the concrete mass out of the equasion. A lot more work and materials however. And $$s.

I use slab only sensors for my bathrooms. It does take some seasonal adjusting, however. Still with this control you need to warm that slab to get any output.

I'm think about a double pour method for climates like yours. I've been talking to a California contractor that does 2" thick overpours.

He has shared a concrete "brew" that he can actually cut, stain and make a crack free final surface with a 2" thick over pour!

I like the heatpump idea. I currently have a demo home under construction with Nudera ICFs, the 2" Nudera underslab package and a ECR GroundLink DX system with a series of wells. Pencils out to be un-believably energy efficient. It will be monitored for two years with seperate meters.

hot rod

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David Zierke

Geothermal wells are good systems, they have a proven track record, but in the college station area you have plenty of heat surrounding you to get by without drilling a geothermal well. Up here in south dakota, we like to have a source of backup heat in case the electricity goes off for a long period. You could get by easily with a RASERS. It would heat your DHW while air-conditioning as well. If you know any good HVAC contractors that would be interested in installing it for you have them get in touch. www.watershotinc.com
The worse part of my suggestion is that without the wells, it pretty much rules out the chance of striking oil. lol

Tom_35

Similar job in Arkansas

Mark,

We're doing a custom home a lot like you describe at this time. I'll describe what we've done if it might help you.

We are using the ECR direct exchange heat pump systems and going with wells. 4 of the 6 heat pumps also have domestic hot water modules to provide on-demand domestic hot water. The units also have the de-superheaters to provide "free" hot water during the cooling season.

The radiant system we are using is Watts and a continuous circulating system is being run. The reason for the C.C. is that our milder winter temperatures tend to have the system cycled off a lot of the time and the floors can tend to cool off.

We are using Tekmar controls and have built control panels for staging the heat. Our first stage heat is the radiant floor heating. In the event that a cold spell sneaks up on us and the floor heat can't keep up, the system automatically switches over to letting the ECR unit start heating via the ductwork. When the stat satisfies, the unit goes back to heating the floor. The heat pumps are staged so only the amount of heat that is needed is used. We also have electric back-up heaters located in the air handlers, but this is for use on if the ECR unit is not operable for whatever reason. The Tekmar controls also alternate which unit is the lead unit and which one is the lag unit, so we are able to keep the earth field around the wells at a more even temperature.

We have a buffer tank on each end of the home (50-gallon electric water heater). The home has 4 mechanical rooms so we are spread out big time. The domestic water will be able to be heated to around 125 degrees and then their domestic water heaters will take the temperature to whatever temp that are wanting.

We used Carrier variable speed air handlers for this job. Since the ECR units require flooded evaporator coils, we had to replace the feeder tubes on the evaporator coils, but this wasn't a big deal.

The radiant consists of in-slab with marble, tile, wood, and carpet; underfloor with Radiant Engineering's plates; whirlpool deck and steps under marble; and a Sun Room with the pex under brick pavers and a wall panel;

We have had the radiant heating working on the home all winter while it is being completed and it has worked well. The owners are looking at a move-in in May so it will be a while before we get to start the cooling.

You are on the right track with the design of your system. As others have said, make sure you get load calculations on the system, deal with someone that knows what they're doing, and invest in something that is going to provide you a payback from Day 1 as opposed to all the good-looking items that you usually see in the nicer homes.

Tom Atchley