All-concrete (ICF) home: Can I make it work with zero or minimal ductwork?
Greetings all, I am a new member that has looked at some relevant articles related to radiant heating and cooling but I am either still confused or in denial of the answer being “not possible in my climate zone”.
I am in climate zone 5 near Chicago, IL. I am building an all ICF home. This includes a basement slab, and suspended insulated slabs for the 1st and 2nd floor and the roof poured at 3/12 and 4/12 with no uninsulated attic spaces.
My thoughts on accomplishing my goal of minimal ductwork and forgoing forced air is to:
Heat and cool with embedded PEX tubing in the slab.
Use a stand alone dehumidification and an HRV for outside air.
If that’s not a challenge, then, I would like to achieve net zero at a later date as well. Therefore I would like to go all electric with an air to water heat pump (manufacturers that I heard of but haven’t had a dialogue with yet included uponor and chiltrex) but I would consider a gas or electric boiler if I could make this system work. (A gas hook up is about 4,400 right now so I would like to avoid that)
I know that condensation on and in the slabs during the humid summers will be my challenge when attempting this set up. Another challenge I know I will face is finding a local contractor that is able and willing to design the details of this system. What other challenges am I potentially missing?
Is it possible to make this work as described? If not, are there sensors and/or monitors available to help? I know anything is possible (within reason) with an unlimited budget but is this going to happen for about 40K?
Systems that I am considering to either supplement or substitute part of the system are:
multiple Mini splits heads
high velocity ducts
pellet stoves
Ceiling fans to move cold air pooling near the floors
The home is just under 4000 square feet, 5 beds 5.1 baths. I am currently thinking of using solar with battery back up to achieve netzero energy. Please let me know if I am missing anything or you would like a picture of my plans to help. Thank you kindly in advance for your time and consideration.
Jim
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Replies
At comfortable interior dew points, slab condensation will not be a problem. But it would waste some energy to run floor cooling and a dehumidifier at the same time. Switching some of the cooling to fan coils would make more sense.
Thanks Jon R for the reply. Regarding Fan coils, this is the first time I am researching it. Are there advantages for me to consider vs using a mini split head? at first glance it seems less expensive at the sacrifice of some control. is this correct?
You will lose some efficiency by having a dedicated dehumidifier that removes latent heat and reject sensible heat back into the room. You can solve that by using a split system dehumidifier like the SD12 from Ultra-aire. However, you will definitely need a dedicated dehumidifier and not a regular a/c unit for dehumidification. A regular a/c unit will not run for very long without any sensible load to remove. If you try and run it without any sensible load the coil will frost up and you'll have a nice block of frost doing no dehumidification. I don't know how they prevent similar problems with the SD-12, maybe they don't and depend on enough sensible load for it not to be a problem.
You will want to keep piping in the floor back from exterior doors to prevent condensation from happening when you open the door and the floor is exposed to a wave of exterior air. A radiant cooling slab can remove about 12-15 btu/h per ft². So keep that in mind when designing your envelope. The minimum floor temperature you can design with is about 66°F.
A air-to-water heat pump/chiller to look at might be the one made by Ecologix here in Ontario, Canada. Contractors price is about $4,200 for their smallest system if you buy directly from them and with the weak Canadian dollar that's about $3,200.
Remember that all your system piping will need to be well insulated and sealed to prevent condensation on the pipes. Insulating all the valves, piping, and pumps adds a considerable cost.
You are unlikely to find a local contractor or even designer who knows how to design a radiant cooling system. They are not very common anywhere in the US. Robert Bean of Healthy Heating website fame (among many other significant contributions) would be your best bet for a design. Finding a contractor to just install it should be much easier.
Reversible chillers w/ fan coils can both heat & cool the place if you wanted to. Anything is possible, but you want the solution to be optimized for both function and cost (up-front and operational.) But right now you're shooting in the dark.
Getting to any sort of optimization of the mechanical systems starts with a room-by-room load calculation (Manual-J or better.)
Chicago's cooling loads are dominated by latent-cooling hours and would be even more so with a higher performance building envelope. See:
https://s3.amazonaws.com/greenbuildingadvisor.s3.tauntoncloud.com/app/uploads/2018/08/30171844/chart.png
https://www.greenbuildingadvisor.com/article/coping-high-humidity-mold
With the high thermal mass of slab floors on all levels the peak sensible loads are going to shrink substantially- they don't need very much chilled water to manage the sensible cooling load, so it will be even more heavily weighted to latent cooling. Chilled water fan coils sufficient to manage the latent loads would probably provide excessive sensible cooling on some days, could be about right for both much of the time, but without running the numbers who knows? This needs to be modeled fairly carefully to get it right, which is why it's a good idea to put some credible load numbers before throwing a bunch of "maybe" solutions at it. A dedicated dehumidifier is likely to be in the cards, but the size & methods that makes the most sense depends on the calculated latent loads & presumed ventilation rates.
Ceiling fans to keep temperature stratification low in winter is the opposite of comfort. The wind chill effect of the fan requires a higher temperature to stay comfortable. With low temp and broad radiant floors stratification issues tend to be very limited compared to high-temp radiators or the even high temperatures of heat sources such as wood stoves,pellet stoves, etc. When heating a room with a 72F -80F radiant floor there's no large source for 100F+ air to be moving toward the ceiling.
Sorry for the late reply. Thank you for your help and advice. Some great points for me to think about. I think finding someone in North America and someone local to install is my best bet. I also got in touch with John Williams at uponor in north Carolina and he gave me some confidence in the prospects of having a functional and reasonable installation. But as you guys recommend a manual J is the place to start.
Thank you again for your time and expertise.