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Heating & Air Conditioning

Radiant Water Heating using Heat Pump

8 years ago

As we live in a Zone 7 area and are building a one story 2000 sq ft on a slab we have decided we want to heat the house with in-floor radiant. We have been told by HVAC specialists that the best solution would be geothermal, followed by hot water heat pump, electric hot water, then forced air heat pump and electric radiant. We don't have natural gas so that is not an option. Geothermal is out as it is nearly three times the price of the other solutions and this is a retirement home.

The second solution we have not heard of. It was described as a heat pump with a hot water boiler that heats or cools the water similar to how a forced air heat pump works but heating and cooling water instead of air.

I am waiting on pricing for this and the electric hot water solution. I found many old discussions on hot water heat pumps but they were small units to replace hot water tanks.

Is the order of solutions logical and what can you tell me about the hot water heat pump solution?

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Comments (8)

weedmeister
8 years ago
I think your HVAC guy is talking about the same thing, a hot water heater that uses a heat pump on top. Say about 80 gallons or there abouts. It would be more efficient than a normal electric hot water heater. They tend to cool the area around them.
jackfre
8 years ago
Check out the Daikin Altherma. It is a really nice air to water heat pump, but of limited size
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"I realize that the HPWH's draw heat from the basement which will be heated by in floor heat but is it significant?" I have a heat pump hot water heater in my basement here in Maryland. The heat pump has no measurable effect on basement temperature, however it does serve to reduce the basement relative humidity 3-5%. The walls of your basement serve as a massive heat sink and changing the room temperature of your basement by operating a relatively small "air conditioner" isn't going to happen. (If your hot water heat pump were installed in an upstairs utility closet, the cooling might be an issue.) In the limiting case of you actually not using any hot water, for example, any heat energy extracted from the basement air mass would be transferred to the heated water sitting in the tank. In the steady state, there would be as much heat being transferred back into the air mass as would be extracted from it. A heat imbalance is created when you use hot water and the heat is lost from the basement system via the heated water going to the sinks and the cold water entering the tank to replace it. My family of two saves about $50 per month compared to my old electric hot water heater. Also, there are frequently tax credits or rebates available.
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Part I You have a very interesting hydronic system, probably gas. However, due to its complexity I strongly suggest that you find someone in your area that is familiar with leading edge hydronic design theory and implementation, including the use of glycol, mixing valves, variable speed pumps, zoning and motorized zone valves. Your system should have primary and secondary loops. The primary loop should have its own circulator. If the secondary loops operate at different temperatures, perhaps the plumbing should be Series Primary Secondary so that the loops/zones further away from the boiler receiver progressively cooler fluid because they’re all in series as opposed to a Parallel Primary/Secondary plumbed system that would have all the loops/zones receiving the same liquid temperature because they’re all in parallel. To not stress the boiler with too great a ∆T, the boiler should be modulating and perhaps a variable speed circulator might be installed with speed variation based temperature differential between its input and output. That way you would have a more constant fluid return temperature at the boiler, less short cycling, greater efficiency due to longer run times and a longer equipment life cycle. IMPO SR
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josey11
Original Author
8 years ago
Jackfre;

Thanks will check it out.
Tamara Boren
8 years ago
Generally I am for convectors rather than radiators. And when they use natural convection and in this way are eco-friendly and use less energy to heat the room - I am for them even more.
lp642
8 years ago
Air-to-water heat pump systems are relatively new and were only made practical by newer high-efficiency inverter-controlled variable-speed compressors. I looked into this a good bit before finally opting for geothermal. These air-to-water systems work better in dry climates than in relatively humid ones where they tend to ice up in winter and have to go through periodic defrost cycles, which detract significantly from the efficiency. So if you're looking into performance specs, you have to make sure that is taken into account. As noted, Daikin Altherma makes some very nice systems, but they are not cheap. If I remember correctly, they were going to be $8-10K just for the hardware, not including installation and not including the radiant piping itself.
Brunon M
8 years ago
I am used to convectors rather than radiators - I have trench heaters from Verano that use natural convection what in my opinion is a really good solution.
ionized_gw
8 years ago
Tamara Boren,

"Generally I am for convectors rather than radiators. And when they use natural convection and in this way are eco-friendly and use less energy to heat the room - I am for them even more."

Do you have some numbers to support the efficiency claim? Convectors generally have to run at higher temperatures to provide heat output comparable to radiators of the same size. With most systems, this would lead to lower efficiency.
fsq4cw
8 years ago
"Geothermal is out as it is nearly three times the price of the other solutions and this is a retirement home."

How much land do you have; is a horizontal loop geothermal HP system possible?

SR

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