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Old 07-12-2015, 09:49 AM   #1 (permalink)
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Default Heat Pump Hot Water Heater

I moved into a ~100 year old fixer upper recently .. one of the 1st issues on moving in was a need to replace the old (not working) hot water heater.

I went with a Hybrid .. Electric-Heat Pump unit.

Electric hot water heaters are very energy efficient ~99% or so of the electricity they consume ends up as joules / BTUs of heat in the water .. but I wanted better.

How to get better than ~99% energy efficient ? ... it has to do with the 'free to me' concept.

A Heat Hump might be in total less than that ~99% energy efficient .. but the majority of the energy input is 'free to me' .. most of the heat energy put into the water comes from heat energy in the air and not paid for energy input .. In heat pump mode the EPA has tested the unit to a yearly average of about ~1/3 of the input electrical energy of a conventional ~99% efficient hot water heat.

Yearly average .. because the heat pump efficiency varies of course under different conditions.

In addition to getting the same amount of hot water for ~1/3 the energy 'cost' ... that cooler air it produces is effectively 'free to me' air conditioning in the summer .. another energy saving benefit.

In addition to both the hot water , and the air conditioning air .. it also at the same time does a little dehumidifying as well .. effectively 'free to me'.

Soo I put it in the basement .. where the dehumidifying is something I wanted anyway .. and the cooler (in summer) initial air temp gives me more available thermal mass 'air conditioning'.

In the winter when I have to 'pay' for heating there are two other tricks .. if the net 'cost to me' ever tips the balance I can always switch it back to ~99% energy efficient electric mode .. I will need less dehumidifying in the winter drier air anyway .. By locating it near the furnace in the basement .. some of the heat leakage that escapes the furnace will get absorbed by the heat pump.

Eventually I plan to also install solar thermal system .. but this unit will act as a nice back up for when there are cloudy cold winter days and the solar thermal system might not produce enough heat by itself.

I will eventually also be modifying the conventional Central AC system to exploit the 'free to me' air conditioning from the hot water heater .. and the thermal mass ground effect of the cooler basement .. etc ... but one step at a time.
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Old 07-12-2015, 11:52 AM   #2 (permalink)
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Impressive!
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Old 07-12-2015, 12:42 PM   #3 (permalink)
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I've been looking into one of these as well. I estimate the payback time at about 3 years if replacing the hot water unit anyway... a little over 5.5 years if you have a perfectly good unit already.
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Old 07-12-2015, 04:34 PM   #4 (permalink)
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I've been looking into one of these as well. I estimate the payback time at about 3 years if replacing the hot water unit anyway... a little over 5.5 years if you have a perfectly good unit already.
I had to replace the old defective one anyway ... and in buying the house the sellers agreed to pay $1,000 of the price of buying and installing a new unit .. Got a Hybrid Electric-Heat Pump unit for $1,140 - $1,000 Seller Credit = $140 of my money.

The delivery / install / and removal of old unit probably the same cost anyway no mater what unit I got .. but I spent another $400 to do that.

My cost = ~$540

To be fair .. the seller offered up to $1,000 probably would have paid for 100% of the delivery , install , etc of a conventional hot water heater .. Soo that ~$540 was the additional cost I had to pay for this upgrade ... but .. So far I'm happy I did .. I suspect in the long run I will be even happier
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Old 07-14-2015, 06:59 PM   #5 (permalink)
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Ive eye-ed those water heaters too. I have a ground level south facing condo and a 28 dollar electric bill. I mainly use ac, celling fans to keep it 68 year round. Its not needing much heat so Ive considered the heat pump water heater to serve 2 purposes. Providing hot water and cooling my home.

I cant replace a brand new perfectly working water heater, so that will have to wait a while.

So, where does the condensation go in that style of a water heater?



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Old 07-14-2015, 07:49 PM   #6 (permalink)
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Quote:
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So, where does the condensation go in that style of a water heater?
There is a condensation outlet on the side of the unit .. 3/8 ID hose fits it fine .. If your drain is bellow that point , gravity will do the rest for your hose to the drain.

My drain was unfortunately half way up the basement wall .. so I hosed it into the condensation pump in the basement.

Quote:
Originally Posted by Cobb View Post
I cant replace a brand new perfectly working water heater, so that will have to wait a while.
They will come down in time .. They are still in the 'early adopter phase' .. just lined up well for me .. and fits who I am as starting to personalize the space.
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Old 08-19-2015, 06:54 PM   #7 (permalink)
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So, any feed back on use? Does it provide any real cooling effort? Any noticeable power savings? Does it run all the time or off and on like the fridge? Does it seem to be all on or off or does it seem to ramp up and down as heated water is needed?

We saved like 20 bucks a month with a timer on our electric water heater. Its on for 12 hours off for 12 hours. We also put a jacket on it and pipe insulation on the exposed pipes.



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Old 08-20-2015, 08:09 PM   #8 (permalink)
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Quote:
Originally Posted by Cobb View Post
So, any feed back on use? Does it provide any real cooling effort? Any noticeable power savings? Does it run all the time or off and on like the fridge? Does it seem to be all on or off or does it seem to ramp up and down as heated water is needed?

We saved like 20 bucks a month with a timer on our electric water heater. Its on for 12 hours off for 12 hours. We also put a jacket on it and pipe insulation on the exposed pipes.
It turns on and off like a fridge.

It seems fairly well insulated and doesn't seem to need to cycle on very often.

I don't use large amounts of Hot Water in the 1st place .. 5-10 min showers .. soo I leave it in Heat Pump only mode all the time .. It takes a bit longer to recover all the hot water in heat pump only mode .. but I never use up the hot water capacity it has anyway.

It isn't a large cooling effect .. but , it's directly proportional to the amount of hot water one uses .. and I don't use a large amount of hot water .. if you use more hot water you would get more cooling effect.

But we can crunch some number estimates to put a 'face' on it so to speak.

There are two ways to do that .. the 1st is probably the easiest .. but also the most crude estimate .. it and an air conditioner are both heat pumps .. While actively heating the water .. it's maximum heat pump rate is about ~550W .. which at most maxes out up around like a ~5,000 BTU Window type (110vac) Air conditioner .. Except the heat removed from the air is stored in the hot water .. instead of being thrown away outside .. but it will only run for as long as it takes to heat the water to the selected temperature.

The second method expands on the above with more numbers .. and math.

It's estimated to use 1/3 of the electrical energy of a resistance based (~99% Efficient) electric water heater to heat the same amount of water the same amount .. soo at least a minimum of 2/3 of that hot water joules coming out of heat in the air that it removed.

Water has a specific heat value of ~4181 J/kgK .. and a density of 1,000 kg/M^3 ... soo .. If the initial input cold water were ~20C (~68F) .. to raise that up to 50C (122F) .. that 30C(30K) change in temperature would take about 125,430 J per Kg of water .. My unit has a 65 Gallon 1st hour rating .. but only holds up to 50 gallons .. which is about ~190 kg of water .. which would be at most about ~23,831,700 J of stored thermal energy in that 50 gallons of hot water .. at least a minimum of 2/3 of that came out of the air ~15,887,800 J .. or ~4,400 wh of heat energy removed from the air ... for every 50 Gallons of hot water per day taken from 20C(~68F) to 50 (122F) ... If it were concentrated over a short period of time that might be allot of cooling .. but it's spread out of the entire day .. and I don't use any where near that .. I use far less than that .. I'm at about 10-20 Gallons a day range .. Soo I might see around ~1,300 wh of air cooling effect over the course of a day .. not allot .. but , a free side effect of using 1/3 of the energy a conventional electric water heater would have used.
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Old 08-20-2015, 08:25 PM   #9 (permalink)
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Thanks, the first one did it for me. So about a 5000 btu window ac unit.

I dont use a lot of hot water either. In my condo I use to turn the hot water heater on for an hour twice a week and had all the hot water I needed.



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Old 08-21-2015, 04:46 PM   #10 (permalink)
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Quote:
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Thanks, the first one did it for me. So about a 5000 btu window ac unit.

I dont use a lot of hot water either. In my condo I use to turn the hot water heater on for an hour twice a week and had all the hot water I needed.
Roughly about a 5000 BTU window AC unit .. running for 1 hour .. for heating roughly ~12 gallons of water to 30C higher temp than it started .. less water or smaller temperature change would pull less heat from the air.
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