Will heat pumps someday run hydronic systems all winter?

D107

From <a href="http://www.heatpumpcentre.org/About_heat_pumps/HP_buildings.asp"></a><a href="http://www.heatpumpcentre.org/About_heat_pumps/HP_buildings.asp">http://www.heatpumpcentre.org/About_heat_pumps/HP_buildings.asp</a>

I see the table says that heat pumps can supply radiators with 55 deg C supply temps. (that's 131 deg F). But what are the outside temp limitations and will that be changing soon? Someone on another thread mentioned some big breakthroughs in this field. If so is residential combustion--even with modcons--on its way out?



Edit: perhaps i misunderstood. I wasn't referring to geothermal applications, but converting the heat in outside air to a hydronic system, like some air conditioners do with forced hot air at the beginning of the heating season.



Thanks,



David

Wayne_16

I just read a brochure on electro industries

doing just that.  Use a air source heat pump for domestic hot water, in floor applications and heat the air.  The phamlet stated they had a new ari classification the this type of equipment.



Minnesota Wayne

D107

another article...

thanks; here's more info:



http://www.richardcollins.net/renheat_aerothermal.html

MarkPFalade

Robur GAHP,,,

Although, it is gas fired.

D107

yes, though a bit large for most residential applications

The one in the attached pdf is rated almost 130K btu. Also it seems to work only in conjunction with a hydronic boiler so it would become quite costly. But the advancing technology might solve those limitations soon.

NRT_Rob

maybe

we are looking at the Daikin Altherma for our shop project and for a client as well.



details are currently pretty sketchy, but it claims output down to -4 Deg F. I'm not entirely clear on what the performance is at that level... first blush seems to indicate 77 degree water at that outdoor temp, something like 95 degree water max.



Most buildings will struggle to utilize temps that low, but uncovered slabs with heavier tubing density, and/or any low temp radiant baseload with an air handler backup could probably make good use of such a unit.



but it certainly isn't going to replace boilers soon. for high temp apps you'd need to have a seriously huge delta-t and use this as a booster.



If robur or others get natural-gas powered heatpumps optimized for smaller loads, you might see some serious inroads there. or if the electric powered units get a bit more aggressive at lower temps. Or, maybe they will follow their air to air cousins and become the shoulder season heater for hydronic systems, transferring to a boiler during very cold weather.



they will definitely fill a niche! but I don't think combustion is dead just yet. 20 years from now and a few more technological leaps later... maybe.

MarkPFalade

Yes,

I have hit them (Robur) up a few times now for a 3 ton model. Their feeble argument is it will not reduce the cost by much so why bother. The rest of the argument goes even though it is rated for 5 tons/123,000 BTUH the design is such that, if set up correctly, it will produce only the exact amount of output necessary to do the job at any given point in time. I find the price to be the limiting factor, especially on the small jobs. The best way I've found so far to set them up is to have a buffer./ hydro separator tank and put the unit(s) on an outdoor reset which is sensing the tank outlet to the structure side of the system. The DDC is a whole 'nother can of worms, nice device and has been reliable, but it could be better. I think them poor Italians rue the day I bought my first set. I've been railing them on the various shortcomings I've come across ever since I took delivery three years ago. Nothing too serious yet, just some niceties like, "Your DDC does everything EXCEPT outdoor reset???" ;-) 

Tom Blackwell_2

Depends on energy cost

I have been experimenting with a 4 ton scroll compressor heat pump with a shell and coil condenser and storage tank supplying heat for a radiant slab system. This has worked pretty well, but falls off significantly below about 38 degrees due to frost buildup on the outdoor coil. The water temperature is set at 115 degrees, and this condensing condition is not too much range for this type of compressor. All that being said; the future will fall out depending on which energy source can do the job the cheapest. If we think as purists and realize that the electrical generation and distribution process is only 27% efficient, and compare the source energy used for each type of energy, then a COP of 4 is better than utilizing natural gas at 90% efficiency, from a gross energy useage standpoint. This could certainly be done with current components, but will require even larger heat exchange surfaces and more first cost than "standard heat pumps". Possibly the best energy ulilization would be to use a gas engine  to drive a heat pump compressor and capture the jacket and exhaust heat.( Think Freewatt). Of course, this has a very high first cost. On top of that, you have various system installers that will sell a heat pump sized smaller than the heat loss of the space in question and install straight electric heat to make up the difference. In this world of first cost avoidance, that makes sense, but gives the industry a bad rap when th homeowner looks at energy cost. I did a lot of number crunching for a residence in Knoxville, Tn. and the best option for energy cost was 2-speed air source heat pumps with high efficiency gas supplementary heat. Of course, that would never fly with a builder. I'm afraid that if natural gas comes back down in price, then all of the innovation we are beginning to see will go away, just like it did in the early 80s.

MarkPFalade

I just finished,,,

an install that included a 16.5 SEER bryant air source HP with a Crown oil fired three pass 86% boiler for hydro air backup. I'm thinking it'll do the trick. It's been relatively mild and it's kind of neat going out there a couple weeks after start up and seeing the oil tank still on the full mark. He says his daily electricity usage is ~ 10 KW. ;-)

Wayco Wayne_2

I recently went

to a Daiken class and they mentioned the next line of the air to water heat pump will be a 2 stage compressor that could achieve much higher water temps. Their goal is to make this a replacement for combustion based boilers. How soon??? We'll see. As we use up our finite fossils this will have to be the norm I suppose. Rob, Dan Foley is currently installing the Altherma for a customer. You should contact him and get his input. WW

MarkPFalade

Oops,,,

forgot we were talking air to water not air to air... ;-)

Economizer

Except that

If we convert to all electric systems we are still using fossil fuels at the power plant and with transmission losses along the way.

NRT_Rob

need to retract my rumour

I misinterpreted some of the sketchy info I got on the Altherma. It is claiming 131 degree max temps, but I can't really believe that at face value... digging more, but I suspect that upper temp range includes significant "backup" heating from the onboard electric backup. but that is just my speculation...

DanHolohan

Gentlemen,

please check the rules about political talk. The Wall is not the place for that. I've removed your posts.



Thanks for your understanding, and your cooperation in the future.

Steve Ebels_3

Disconnect in reasoning............

If we convert to all electric systems we are still using fossil fuels

at the power plant and with transmission losses along the way.



Exactly. It is astounding to me to talk to people who have no concept of how power is made and delivered.