Air Conditioning - Radiant heat with ac

Hi,

I am in the process of building my own home and I am considering the use of a combined system. I want to have a radiant heating system for the entire house made of 5 zones, I have priced the system up and done some extensive research into this, it will be an oil fired system with the tubing buried in a concrete floor. I will also be using an indirect fired water heater which will use the heat from the radiant system to heat the domestic hot water. Important note is that the house is going to be built using ICF's for all exterior walls and for the concrete floor between the basement and the main floor.

The thing I am just beginning to research and need some help in understanding is that I am also going to want to cool the house down. So an ac unit is required - but how would the two systems interact? I know I do not want the ac doing any of the heating work so out goes the heat pump, I want the cooling to be as uniform as possible and I have heard of systems where the cooling is sent from the floor and exits through the ceiling. (Not sure of the technical name). So can anybody tell me how I tie this all in? Is it done by the thermostats in each of the zones? Can a single thermostat control both heating and cooling as seperate systems? I would hate for the heating and ac systems in my house to start a competition as to who gives up first :)

Any responses greatly appreciated. Many thanks

Wayne

Loops in the floor won't help you when its time to cool. You could use above floor fan coil units and blow air over the coils. In the winter the coils would have hot water circulating in them. During the summer the same coils could be supplied with chilled (40 degree) water. You would then have plenty of heat AND cooling. The only drawback is that you would be required to have a hot water (hydronic) heater and a chilled water unit. A set of valves would also be required so that you could change the water system between heating and cooling. The system would work very well, but would be expensive to install. I've seen systems just like that before, but not in houses.

If you are going with hydronic infloor heat the only feasable way to have a/c is to have ducting ran and an a/c only unit installed. This system can be zoned but it takes alot of knowledge to do it right so when you get your bids check refrences.

The problem with them fighting would be simple with interlocks. One would not be able to run if the other was on.

This is similar to the plan I'm working on for my next house. Yes, one thermostat can control 2 different systems. Hydronic for heating and forced air for cooling, but 5 central a/c units is going to be a bit expensive up front. Another thought might be to use mini-split systems or wall units for cooling, but there would be separate thermostats and always a chance that the heating and cooling would fight each other. I'm hoping to go with a geothermal heat pump that can provide hot or cold water which will be pumped through either the floor for heating, or an air handler for cooling. I'm still a long way away from this dream so I haven't got any numbers on paper. Please let me know what choices you end up with and how they work when they're finished. I'm very interested in your whole project. Where are you located? What ICF manufacturer are you using? What type of roofing?

Doug M.

Wayne You dont say where you are first that helps.Then how many sq ft in the home or close to it that helps . It all has to do with what you have there for what is the best way to go. Id say for now AC duct unit or units in the attic You can work witch one will be on at one time and heat in the floor.
On the search of your ICF home I see that the R value is R-25. I have a all cement wall home here. called a Royal Wall have been around for years. It rates a R-28 for insulation. Takes about 6 hr to set all the outside walls for a 2200sq ft home. "just info"


ED :confused:

Ed, Interesting info on Royal building systems. I had no idea they existed. Looking at them, they're basically the same idea as an ICF only without the integrated insulation. Different ICF systems have different properties. Some have better insulation values than others, but some contain more mass and, despite a similar insulation value, will retain temperature better. Royal should be included in the running with the other ICF's as should Rastra which also makes a slightly unique system along the same lines as ICF. There's also a system that encases insulation on the inside of 2 sprayed on layers of concrete. Haven't heard much about that system yet. Some of the ICF suppliers are also starting to come out with concrete insulating roofing systems - Carry the tightness, mass and strength over head as well.

Wayne You dont say where you are first that helps.Then how many sq ft in the home or close to it that helps . It all has to do with what you have there for what is the best way to go. Id say for now AC duct unit or units in the attic You can work witch one will be on at one time and heat in the floor.
On the search of your ICF home I see that the R value is R-25. I have a all cement wall home here. called a Royal Wall have been around for years. It rates a R-28 for insulation. Takes about 6 hr to set all the outside walls for a 2200sq ft home. "just info"


ED :confused:

ED - The home is going to be built in Maryland and has a total of 3800 sq ft using Reward Walls ICF Forms. I have all the forms now and I am in the process of getting ready to dig out the basement. The specs I have on the wall forms are:

Actual R-value of concrete & iForm: 24
Effective R-value of concrete, iForm, air infiltration, and thermal mass: 32+
Air changes per hour -- .04 - .09

I was thinking of running the oil fired radiant heat system ( http://www.southernradiant.com/pages/1/index.htm ) for heat and the a/c unit for cooling (Something like a Trane a/c unit with ducting both being controlled by a single thermostat for each zone (5 thermostats in total). To control the temperature in each zone the radiant system will have a valve to permit the heat through and for cooling I thought of using something like an electric duct volume damper. The thermostat would need to be setup so that a max/min variation could be set. Say 5 degree's in that if the temp was 65 then switch on heat up to 75 - then the cooling would only initiate if the zone got warmer than 80. This would prevent the two systems from battling it out heating and cooling the zone at the same time.

Is what I am proposing to do so unusual? Surely with the radiant systems being used so often now; a way has been developed to incorporate ways to heat and cool using both radiant and a/c. I am not about to throw tons of cash at this to have the latest geothermal gimmicks but I do want a reliable and comfortable system that is not overly complicated.

By the way - if you want to get any insight into my project then visit http://www.wayne186.com/selfbuild I need to do some serious updating as things have moved along a bit since the last update.

Zoning the forced air a/c is not unusual but doing it in 5 seperate zones will be costly and like I said you can't just close off the boxes. There will almost have to be like a dual duct system and when the box closes it diverts it's air into the return duct. That way if only 1 zone is calling you've still got the necessary airflow through the system. To add to it the boxes will need to be accessible for future service.

38K sq we would only do about just two units for the home . Not long ago did a 46K with 3 units. I have done a home with up to 8 AC units in it but it was big.
5 zones on a AC you could put one high side and 5 coils one in each zone. That work real good.

5oF for auto change over . It dont work--- in parts of the year you will have over runs that will turn on the heat and then back to the AC.

5 zones in 3800 Might be ok for heat. If you want put insulation in the inside walls so you can keep them different. But for cool dont think you need much up there. But for that size home Id say just one or two units at the most. With an AC its more in get the humidity out of the home than a temp drop. That way you feel cool. With 5 different zones in the AC. I cant see how you would get the humidity out.

just my .02 cents
ED ;)

Like Ed said you could just go with maybe 2 units and if it's all sized right esspecially the ducts all rooms will be comfy.