[Greenbuilding] Heat pump HWS

[Antonioli Dan]

Some states (in the United States) have apparently banned electric hot water tank heaters, limiting them to heat-pump only. My hydronic supplier told me that his brother lives in Texas and recently replaced his hot water heater and discovered that they could only buy a heat-pump hot water heater (gas wasn’t an option), and they are complaining about the recharge time. I’m looking into hybrid models that allow you to program the tanks to run on heat-pump only, electric only, and both. 

The electric solar thermal tanks have one electric 4500 watt element and two additional dip tubes. With roughly 80% of the heat coming from solar and the remaining 20% coming from grid-tie solar you can easily achieve net-zero energy hot water. 

But with heat pumps now all the rage what I’m looking for are solid numbers, not hypothetical calculations. Real-time testing. How much electricity do the heat pumps use? If you use them in hybrid mode can you achieve the same degree of efficiency and net-zero energy as a thermal system?

Neither Rheem, my hydronic supplier, or my solar thermal contact (with 35 years of thermal experience!) have any real-world experience. Rheem sells both thermal and heat pump hot water heaters but their “technical support” division is clueless!

Dan



On Apr 21, 2016, at 9:32 PM, Nick Pyner <npyner at ihug.com.au> wrote:

> Indeed I have.  I was unsure about raising them because of climate considerations, but the essential principle is the same anyway. It's just a matter of a PV-powered resistance heater, or a PV-powered heat pump.  If the latter is a practical option, it's a hell of a lot better one, and means the PV power available can be deployed elsewhere.  
> 
> Our state certification is a little bit rough'n'ready in this arena, but heatpump is rated highly.  Standard resistance heating was simply banned from new construction for some years. It then quietly came back on the lists some time ago but, while they don't actually say so, I suspect you have no chance of getting a pass with it if you don't have some PV. On the other hand, including PV absolves you from all sorts of sins - resistance heat electric storage HWS included.
> 
> Heat pump HWS have attracted some controversy of late with claims that the capital and maintenance costs may outweigh the savings. I don't believe it. The tank may well fail before the fridge gear does. I don't know much about them and I would be more worried about noise. 
> 
> Nick Pyner
> 
> Dee Why NSW
>>> Antonioli Dan <solardan26 at gmail.com> wrote:
>>>  
>>> 
> heat pump?
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