ERV with cooling and humidity control
jesterblackdog
| Posted in Mechanicals on
Hello All,
I’m planning my new super insulated Zone 5 home and it will definitely have some kind of energy recovery system but I see some integrate supplemental electric heating, cooling and/or humidity control. Since my heating solution will be floor radiant, I am interested in cooling and humidity control. I would love to avoid mini-splits for the cooling solution.
Does anyone have experience with some integrated systems out there or is it better to have separate mechanicals for each function? Any systems or manufacturers to recommend or to avoid?
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Replies
JBD,
Are you open to rethinking your HVAC plan? Radiant doesn’t make a lot of comfort or economic sense in a well built house. Mini-splits are often less expensive and more flexible. It also free of dollars for ventilation and humidity control, both of which you’ll probably need to manage indoor air quality.
I am open but I'm trying to avoid min-splits because I don't like blowing air heat and they are not appropriate for segmented spaces (like bedroom areas). My primary motivation is not cost savings.
When designing the radiant system keep the water temperature as low as possible. In zone 6, my house typically runs at 93F...I use a water heater for the Heat. For ventilation system, I would look at a Hydronic Air Handler such as https://www.hi-velocity.com/ That coupled with an Air-to-water heat pump should provide a very efficient system.
The hivelocity system has nice programmable VFD so you can optimize the ventilation.
William, thank you for the input - especially from someone with the system I want! What do you mean by " I use water heater for the Heat"?
The manifold feeding the Warmboard is connected to the Domestic Water Heater - through a Taco Heat Exchanger (XPB). That takes 140F water from the Tank and exchanges it with water below 95F.
In theory it makes a lot of sense to have humidity removal on ventilation air--it takes less energy to remove a liter of water from the humid incoming air than it does to remove it from the less humid inside air. If you do that in a house that has exhaust from bathrooms and kitchen, you might be able to get away with that as your only dehumidification. One way to do it is with a "magic box" that replaces the heat exchanger with a heat pump, but I'm not convinced that that makes sense--a counterflow heat exchanger is almost a free energy source and you aren't getting the full benefit of that when you go to a magic box. I recommend instead putting a fin-coil heat exhanger inline with the supply air, so the fresh air that comes out of the ERV goes through that before splitting off to the supply vents. You'll then need to run very cold water in that to get the dehumidification you want, and more modest temperatures in the floors, although you might never need that--the cooling through the supply air might be enough, depending on your climate and solar gain. The same air-to-water heat pump that supplies your floor could supply the chilled water for that, but you'd need some tricky dual buffer tank and control system to have the same heat pump doing different temperatures for the floor and for supply air.
But I would advise having a backup plan if that doesn't give sufficient dehumidification--perhaps a few spots you can install small fan-coil units for more conventional cooling, or being prepared to add a dehumidifier.
Charlie, do have a good source to get educated on "small fan-coil units"? Is that simply a coil with cold water to condense out the water in the passing air?
Also, why do you say it's easier to remove the humidity from the high humidity incoming air than the lower humidity indoor air?
Thanks
I think what you're looking for is a conditioned ERV, or CERV. See https://buildequinox.com/
DCContrarian,
Thank you for the link. I actually know this company because a close friend put one of their units in their house in Vermont. The company has since added features and sophistication. I need to dig deep into their product - it looks great on paper. I wonder how they are for actual operation reliability, efficiency etc. Do you have direct experience.
I would suggest looking at cast iron baseboards. Weil McClain makes one called SNUG. It doesn’t fit every style of house but I think they are the best delivery method for hot water heat. While I have found that people are still comfortable with infloor heat in pretty good houses, even with the lower water temps, in floor can be difficult to match up to a room by room load calc. Usually in floor loops are spread evenly through a house meaning you get pretty much the same BTU per foot everywhere. Most new houses have skewed room by room loads. There are often areas in new houses with higher or lower BTU/square foot than others. This can be overcome with zoning but that gets tricky to install and requires additional controls or pumps. Baseboards are great because you can size them by the foot to match your room by room load targets. Cast iron will require moderate water temps which still allows for true radiant heat. The water temp is usually in the sweet spot of giving you some radiation while still keeping your boiler running at good condensing water temps. Fin tube baseboards are attractive due to cost and can give you the same ability to match sizing requirements but they operate at much higher water temps which reduces boiler efficiency but also gives you more convection type heat which is less comfortable. A high efficient boiler with cast iron baseboards coupled with a ducted mini split for cooling would be a great system. The ducts needed for the air handler would give you a lot of flexibility for your ERV/dehumidifier.