Heat Pump System Options – radiant hydronic floor plus ducted air
As a follow up to the advice I got on this thread I have a few more questions. https://www.greenbuildingadvisor.com/question/cold-climate-air-to-water-heat-pump-auxiliary-heat-ac
Subject structure is 3BR cottage outside Rangeley, ME climate zone 6.
In typical fashion, the building project is behind schedule, but we do have a foundation in and framing has started. The lower (basement) level and garage slabs have pęx tubing for heat. For cost and simplicity, we’ve decided to go with ducted air for the first floor heat & A/C and also to provide air conditioning for the lower level (no A/C in the garage).
The prior thread advised that air to air heat pump systems are more efficient at cold temperatures than the air to water systems. For a variety of reasons including cost, complexity and available volume I’d prefer to run everything off of one heat pump system with propane backup.
I’ve found lots of information and available products for air to water heat pump systems that can support the slab hydronic radiant floor heat and a ducted system (heat & AC) with a coil insert. I can’t seem to find any information about an air to air heat pump systems that can also support the hydronic floor heat? I’m not sure what I should be calling the device? Does such a system exist? I’d expect I’d need both a propane boiler and furnace in this example?
Appreciate any and all thoughts!
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Replies
Air to air heat pump to support hydronic? I suppose it could be done... In theory.
But why?
To be clear, are you asking for an air to air heat pump that then has a sort of fan coil unit that transfers the heat from the air to a hydronic loop?
I'm just a bit confused by your questions...
What you are looking at is possible but only in the commercial world. LG Multi V units used to offer a water coil that would essentially work as zone some any indoor unit. This is mega$$.
I think the simpler option is to stick with the air to air for heat and cool and use the propane for the floor heat and backup.
You can put a hydro coil connected to the propane boiler on the outlet of the heat pump indoor unit and use that for backup.
So this would run. Heat pump for bulk heat, propane for floor heat most of the time. Propane floor heat plus coil for backup.
Now if you want to DIY, there is nothing stopping you from putting say somehting like this:
https://packless.com/products/condenser-wshp-coils/coax-2201-j
In line with the heat pump air handler refrigerant feed. This would let you tap off some of the heat and use that as a refrigerant to water feed for your floor heat loop. You would have to watch how much heat you are taking to avoid too cold of outlet temp on the air handler but that is about it.
Thank you for the Multi V, that was the name I was trying to remember in my post #3 below.
How much are those Wolseley coils? Their website won't show me pricing. It's an interesting idea. Somewhere I once saw a blog post about putting a coil of 3/8" copper tubing in a barrel of water to get something similar. I've also seen people try it with flat plate heat exchangers.
Couple hunderd. Cheap enough that I'm tempted to try this combo air to air with hydronic sidearm.
Won't heat DHW with it but should be enough to have a couple hundred sqft of floor heat.
LG makes a multi-head air-to-air heat pump where one of the heads can be a hydronic heat exchanger. The name escapes me right now. We've discussed it here, my recollection is that it was hard to get. But it does exist.
When you say you want to have a heat pump with a propane backup, what does that mean? Because there are three possible configurations:
1. The heat pump is undersized and the propane supplements it when its capacity is insufficient.
2. At a certain temperature the cost of propane is less than the cost of electricity and you want to switch over completely below that temperature.
3. You want the propane to provide heat when the electricity goes out.
These three uses cases require different implementations.
I'm not a fan of #1 or #2, especially in new construction. Just size the heat pump appropriately. The money you'd save from switching over will never pay back the additional equipment and complexity a multi-fuel system entails.