AC System for Home with In-Floor Hydronic Heat
For a new construction in Southern Ontario the desired (non-negotiable) heat source is infloor hydronic heat (warmboard).
What would be a robust AC supply? 2,500 SQF, 2 floors, above ground (no basement). Sensible cooling load calculated at 38MBH 1700CFM. No open floor plan, all areas isolated with doors though naturally many doors will be open much of the time in practice.
The insulation is above code, but not passive house level. There is a fair bit of glazing.
Do not mind some duplication (e.g. installing mini splits and running them to cool only and as a backup for heating should hydronic in floor fail or need a boost.
Ideally prefer electric, though have access to NG.
Heat pumps are an option, but noise is a major concern. Mechanical room is close to living quarters, so for example air source hot water heat pump is not attractive due to noise, so considering electric resistance heaters instead – just an example.
Have no stomach for uncommon systems (e.g. Chilltrex) or to get hydronic cooling right (e.g. Tekmar), prefer something robust that has better odds of being readily installed and serviced.
What is the robust, affordable, and quiet (this is important) AC option?
(1) Mitsubishi Zuba heat pump ducted (have tentatively 3-5 distinct zones).
(1a) Mitsubishi air source heat pumps cooling only, install several ductless, and a couple of multi-ducted ones?
(2) Jaga Briza units?
(3) Something else?
I have an HVAC consultant, but cannot tell if I am getting “have a hammer, looks like a nail” advice or if my multiple criteria (hydronic infloor heat only, quiet AC, robust system without full duplication) are too complex to result in any sensible options?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
The guy shouldn't get hung up on the radiant floor heat, just think of it as radiators and install what you would if you were called upon to install air conditioning in a house with radiator heat. If you're not willing to be experimental there's no opportunity for integration and you're going to have two separate systems.
Where there is an opportunity for integration is with ventilation and dehumidification, which you will need in your climate. You definitely want a system that is ducted for both both conditioning and ventilation, especially in a house that is split into many rooms. Run away if he suggests ductless.
Thank you. The ERV is planned, but the issue of "ducted" - vs ductless (multiple") seems less clear.
The large ducts for full-on "forced-air-style" AC vs short smaller ducts from indoor unit of splits - vs simply in-ceiling ductless for larger spaces plus multi-split short ducts for several rooms?
(I do not like ducts).
Are you using the Warmboard Comfort System(WCS) in the Heat pump or boiler version. The WCS is limited to Two zones of cooling. What heat pump is being specified? The mono bloc are installed outside, I would look for something rated in the 55 DBA range.
For my PGH (still under design), I have Warmboard as the sub floor with a Briza-12 in the great room to avoid ductwork. The Building Equinox CERV2 or Minotair ERV provide almost enough cooling for the bedrooms. So I am using a room by room heat loss/heat gain calculation to see what needs to be tweaked in terms of insulation or windows. Uponor Xpress Trak could be used in the ceilings to remove any heat. This looks similar to the Messana NK panel.
For controls, look at the HBX THM 0600/ZON 0600 which do both heating and cooling.
I would start with a room by room heat loss calculation to help size the equipment. A properly designed duct system should not make noise.
Your requirements are pretty confusing, you’re asking about AC then mention heating a bunch.
AC is easy - a fully ducted approach is the most comfortable solution. I’d reflect if you truly need zones, but other than that, fully ducted is great. Any manufacturer will do, a variable speed system is better than single speed. If you don’t want an air to water heat pump, then this system will be totally separate from the radiant floor. You can then decide if this will be just AC or if you want to include heating with it too. Ductless will be louder and less comfortable/robust.
Thank you. I am mentioning heating in part because I am looking for AC-only solution (the hydronic floor heat is non-negotiable). Ducted AC with a heat pump has heat redundancy in case of a - for example - mitsubishi ducted multi-split heat pumps as they do not come in cooling-only mode (only ductless ones do).
Additional reluctance for a "fully ducted" is some loss of space to accommodate large ducts (it lowers ceiling in one area - not everywhere - but still).
I understand high velocity AC may be louder than a fully ducted large ducts ACs, but I did not think ductless AC is louder?
Deleted
Ductless AC is louder. I have ductless and ducted in my home. Ducted is silent to my ears. Ductless has beeps and vanes and fans.
For the warmboard, the proposal was for a natural gas powered combi boiler, which I do not want. Then air to water heat pump was proposed (Smith, Bradford, and I am forgetting the third option) - all had a fairly high decibel rating, which did not appeal, so now the quest is for electric only or something else or back to combi and natural gas which I would prefer to avoid.
AC quest is parallel. I am aware of Nordic and Arctic and Solstice that may achieve both radiant heat and cooling but (1) worry about noise (2) cannot find many reviews.
That’s scary - AO Smith and Bradford white heat pump water heaters are for domestic water heating, not radiant floors. They cannot heat your home so I have no idea why those were suggested.
Electric options are air to water or water to water if you want to keep the radiant floors. Both are uncommon in the US but maybe less so in Canada. If your electricity is cheap enough, an electric boiler could be an option. It cannot provide cooling.
You are right - my mistake. Those were for Domestic hot water (instead of combi boiler).
Electricity is cheap enough.
An electric boiler would work for the application - they’re quiet and simple. They’d use about 3x more electricity than a heat pump but cost much less upfront. If your rates are in the ~$.10/kWh range it’s worth exploring.
The electricity rates are interesting:
Ultra-low overnight rate of 2.4 cents per kWh: everyday 11 p.m.-7 a.m.
Mid-peak rates of 10.2 cents per kWh: weekdays 7 a.m.-4 p.m. and 9 p.m.-11 p.m.
On-peak rates of 24.0 cents per kWh: weekdays 4 p.m.-9 p.m.
Weekend off-peak rates of 7.4 cents per kWh: weekends and statutory holidays 7 a.m.-11 p.m.
It is very tempting to try to program the system (both heating a cooling) to avoid the 4pm-9pm window which makes electrical attractive. E.g. larger water tank for both heating and DHW ought to help?
I have not discussed this aspect with anyone yet. But it is a factor.
These rates support doing exactly that:
Off: $/MMBtu = $.024*293 = $7.03/MMBtu
Mid: $/MMBtu = $.102*293 = $29.89/MMBtu
Peak: $/MMBtu = $.24*293 = $70.32/MMBtu
It will involve a lot of storage, but that's cheap electricity!
If your heat loss is 50kbtu/hr (Guessing!), you'll use about 37,000 kwh per year based on London, Ontario. If evenly spread across all hours, that's ~$3900 for heating. You can get buffer tanks that are about 120 gallons, which can store about 29kwh each if you can heat the water 100 degrees higher than you'll need for the floor. The max kwh you'll need for the 16 not off peak hours would be about (50000*16/3412) = 234. I wouldn't store all of that, but about half that looks pretty good. That'd be 4 120 tanks. In reality, the peak hours should have less heat loss, so costs should be even lower. Are 3-4 buffer tanks + electric boiler cheaper than an air-to-water heat pump (with 1 small buffer tank)? That's unclear.
For warm floors, using an electric boiler and radiant tubing is much more complicated and expensive than just running resistance wires under the floor. You really gain nothing from the radiant tubing.
I would size the heat pump for the cooling load, and get one that does heating as well. Then install as much floor heat as you need to meet your heating load (I'm assuming you're in a heating dominant climate and the heat pump isn't going to meet all of your needs). Pay close attention to how your heat pump derates as the temperature drops when calculating sizing.
Then it's your choice of which heating system to use as the primary and which as the backup. The heat pump is cheaper, the floor heat is nicer. You could even have them on separate thermostats with different time schedules, so the heat pump is primary when electricity is expensive and backup when it's cheap.
Very good point! I guess it provides the future optionality of air to water, but is otherwise complicated and expensive.