Using a mini-split for both air cooling and hydronic floor heating

[theoldwizard1]

This concept seems like a perfect solution for heating and cooling a garage or other area (likely under 1000 sq ft) with a concrete floor. I'm certain this has been done. It is an obvious extension to heat pump technology. No "new inventions" required.

However, none of the major brands of mini-split seem to offer any type of heat exchanger for creating radiant floor hot water. A bonus would be heated forced air for quick warm up. Balancing floor temp and air temp could be a challenge.

What am I missing ?

[jeff5may]

Look into the European market. They have been using hydronic systems much longer and more efficiently than the USA. A high emphasis has been assigned to alternative and innovative technology in building science across the pond.

Most homeowners in America are still coached into some sort of forced air gas or straight electric heating system by the industry at large. Even though it is almost always more energy efficient to use a heat pump system, due to the large natural gas resources in America the dollars favor natural gas. Therefore, even when hydronic systems are employed, a gas boiler is the heat source of choice.

That being said, there are many domestic manufacturers of mini split and full sized heat pump systems in the USA. You just have to hunt for the hydronic loop configuration and do lots of research on the subject to find a setup that will work for your site. All of the major manufacturer s have their flavor to sell you.

A good portion of the offerings are marketed as commercial products. Office space zone based water source units are common in the commercial sector.

[theoldwizard1]

Originally Posted by jeff5may

Most homeowners in America are still coached into some sort of forced air gas or straight electric heating system by the industry at large. Even though it is almost always more energy efficient to use a heat pump system, due to the large natural gas resources in America the dollars favor natural gas. Therefore, even when hydronic systems are employed, a gas boiler is the heat source of choice.

There are a few places in the US (and Canada) that do NOT have gas piped down their street.

A good portion of the offerings are marketed as commercial products. Office space zone based water source units are common in the commercial sector.

That is the only place I can find it from Mitsubishi, but the compressors are too large.

[jeff5may]

There is a very miniscule market for hydronic heating in general in the USA. The industry is geared 99.998% to sell central ducted systems. The remaining 0.002% of systems sold are divided between boilers, mini-splits and hydronic/solar/biofuel/other. I'm sure that air-source hydronic systems are in the very low parts per million in unit sales.

We are literally spoiled rotten by cheap energy! Literally the second thing I hear people ask about the subject in general goes something like this:

"You're telling me this $5500 system is going to save me only $35 a month??? Bah!"

An armchair calculation from another ecorenovator (thanks BBP):

My Cost of heat (per 100,000 BTU)
$.16 / Kwh Electricity = $4.69
$.78 / Therm with 85% Efficiency NG boiler = $0.92
(He figured any installed heat pump boiler would need to operate above a COP of 5 to be cost effective vs. a NG boiler)

Check out:

Daikin Altherma

NorAire

Nibe

Hydronic Furnace w/Heatpump

[theoldwizard1]

Originally Posted by jeff5may

We are literally spoiled rotten by cheap energy!

well I have to agree with you there !

I'm sure that air-source hydronic systems are in the very low parts per million in unit sales.

I would say zero when it comes to mini-splits !

I do understand, that a mini-split heat pump has limited practical application, but a garage or large 1-2 room addition, IMHO, is a perfect candidate for one.

Most mini-split compressors now have 2 - 4 sets of ports so multiple indoor units are simple to install. Adding a hydronic heat exchanger to the suite of indoor units that each manufacture sells seems like a "no brainer". There are several suppliers of refrigerant to water heat exchangers that could be used. The only thing the company would have to do is provide the appropriate sizing charts to their installers.

[F357]

Originally Posted by theoldwizard1

Most mini-split compressors now have 2 - 4 sets of ports so multiple indoor units are simple to install. Adding a hydronic heat exchanger to the suite of indoor units that each manufacture sells seems like a "no brainer". There are several suppliers of refrigerant to water heat exchangers that could be used. The only thing the company would have to do is provide the appropriate sizing charts to their installers.

It would be fantastic if they made a pool heater unit also. Here in the NW a swimming pool is barely usable for a month without heat. But the air conditioners all pump heat into the air for 4+ months a year!

But who needs MFRs, anyway? If you want that, make it. If you can't make it yourself have your A/C guy do it for you. The parts are on the shelf, just need to be creative.

[theoldwizard1]

Originally Posted by F357

It would be fantastic if they made a pool heater unit also. Here in the NW a swimming pool is barely usable for a month without heat. But the air conditioners all pump heat into the air for 4+ months a year!

I'm pretty certain that you can buy a commercial unit like this !

The problem is, you have to run the A/C to heat the pool. In the NW, how many days in May and September do you run the A/C ? But, I am certain that you would run the "heater" for the pool some days even in June, July and August ! This should really reduce your A/C electric consumption on those days.

Originally Posted by F357

But who needs MFRs, anyway? If you want that, make it. If you can't make it yourself have your A/C guy do it for you. The parts are on the shelf, just need to be creative.

I agree ! One problem is sizing the heat exchanger. On the compressor end for the pool heater and on the end of of one of the indoor lines sets for the other.

The second problem is feedback/temperature control. On the pool heater, you probably don't need any controls, just crank down the temperature on your inside thermostat when you want to heat the pool ! Do NOT run the filter pump when you do not want to heat the pool water. Maybe add a pressure/temperature relief valve in the water circuit at the heat exchanger. I am surprised that this addon is not more popular.

Temperature/feedback from the hydronic heat would be much more difficult, especially with modern computer controls and wireless thermostats. (Where is that universal heat pump controller when you need one ? )

[jeff5may]

Im working on it. To satisfy the anticipation and end the suspense, I will post a few sketches that have reduced functions. That way, everyone interested can slap in a controller and start fiddling. Then when we have a robust sketch, it can replace the preliminary release.

[NiHaoMike]

You can install a plate exchanger in the vapor line, along with a thermostat to turn on the pump when the line gets above 90F or so.

[F357]

Originally Posted by theoldwizard1

The problem is, you have to run the A/C to heat the pool. In the NW, how many days in May and September do you run the A/C ?

Actually I run it pretty solid through September. Gets spotty about the beginning of October. Even if you just throw the cold away they should make small/portable heat pump pool heaters, like they do for water heaters. Seems like there would be a market for this?

I'd also love to see a fridge and deep freezer somehow worked into this system powered with cold air that would otherwise be thrown out.