[Greenbuilding] HEAT PUMP WATER HEATER

[Paul Eldridge]

Hi Alan,

I just purchased a Nyle heat pump add-on to supply heat to the side arm 
attached to our oil-fired boiler.  It's a 115-volt system that draws a 
maximum of 800-watts and has a rated heating capacity in the order of 
1.8 kW (6,275 BTU/hr). This one can be used with an electric, solar, 
gas, oil-fired or indirect water heater (the Geyser RO) but there is 
another version designed specifically for electric tanks (the Geyser R).

See: http://i362.photobucket.com/albums/oo69/HereinHalifax/Img_1914.jpg

The cost of the Geyser RO is not unreasonable at $1,150.00 CDN (the 
electric-only R model is cheaper).  Installation is pretty straight 
forward and you don't have to discard your existing tank or modify your 
plumbing.  The fact that it works in conjunction with your existing 
water heater also eliminates the risk of hot water run outs or sub-par 
performance in the sense that if your electric or oil-fired water heater 
can keep up with your DHW demands today, it will be no different 
tomorrow or the day after, except that the Nyle will presumably take 
over the lion's share of the work.

Another nice thing for us is that the Nyle will supply us with all the 
DHW that we require (at about one half the cost of a conventional 
electric water heater) *and* it will provide us with "free" 
dehumidification.  As it stands now, I run our dehumidifier eight months 
of the year, seemingly non-stop some days, and so this responsibility 
will be handed over to the Nyle, in whole or in part (the outdoor 
relative humidity as I type this is 100 per cent); in effect, we'll 
receive two services for the price of one.  In addition, we'll have the 
added benefit of free coolth during the summer.  But what about the 
winter months you ask?  I'm not overly concerned.  Our home is heated by 
two high efficiency ductless heat pumps that supply us, on average, two 
and a half to three kWh of heat for every kWh they consume.  The Nyle 
will "steal" some of this heat to heat our DHW, but we're still way 
ahead in that the heat we sacrifice will have been provided to us at as 
little as one-third the cost of electric resistance.

At the moment, our DHW is supplied by a small 70-litre 115-volt/1.38 kW 
electric tank that was originally intended to pre-heat the water feed to 
our side arm.  We wanted to minimize the amount of oil that we consumed 
for hot water purposes and the electric tank did cut the runtime of our 
boiler by roughly two-thirds.  Then, rather than let the side arm call 
for heat at will, we decided to limit the boiler's operation to a single 
ten minute run twice a week, and eventually cut that to once a week. 
Ultimately, we decided to stop using the boiler altogether, which means 
that we have to pull enough hot water through the system to offset the 
standby losses of this larger second tank. Consequently, we take 
somewhat longer showers than we would otherwise, wash our clothes in hot 
water and occasionally open up a hot water tap for no good reason; if we 
don't, the supply temperature falls off rapidly and we experience cold 
showers. Since we'll be using the heat pump to heat the water stored in 
the side arm, we can now remove the electric tank from service and 
eliminate this needless usage.

Presently, we use an average of 4.0 to 5.0 kWh a day for DHW purposes 
and I anticipate that our new Nyle will cut that by more than half -- 
not a huge savings by any means, but still worthwhile from our 
perspective.  First of all, we'll eliminate the standby losses of the 
electric tank which at 47-watts works out to be just over 1.0 kWh a 
day.  Secondly, we'll no longer need to wash our clothes in hot water 
and can eliminate the other steps we take to prevent the side arm from 
cooling off.  The additional heating demand during the winter months -- 
perhaps 3.0 kWh per day which translates to 1.0 or 1.2 kWh actual with 
respect to our two ductless heat pumps -- will be offset in large part 
by the reduction in runtime of our dehumidifier come spring, summer and 
fall.

I'll have power monitors installed on our Nyle and our two ductless heat 
pumps and will log this data in a spreadsheet so that I know precisely 
how much electricity is consumed by these three appliances on a day by 
day and hour by hour basis.  I'll provide the list with occasional 
updates once I get the unit up and running.

Cheers,
Paul

>
>Alan Abrams alan at abramsdesignbuild.com wrote:
>
>need help quantifying the (presumed) benefit of using a heat pump water
>heater for a new, airtight house, passive house insulation and glazing.
>There is no natural gas serving the site.
>
>the cooling load is very low--the house is surrounded by tall trees--but it
>will have a Wash DC latent load.   The trees compromise the potential of
>solar thermal...
>
>...so the question is, does the efficiency and modest dehumidification
>capacity of a HP WH offset the extra heat load, compared to either a
>straight elec resistance WH, or bringing in propane service?
>
>-a


Alan Abrams*