Hybrid Water Heater

[tigerwillow1]

I don't see how these things are of any benefit at all in the winter. If in the house, any heat they transfer to the water gets pulled from the house, and you have to replace it with more heat to the home. If in the garage, they will make the garage even colder than it already is. In the summer these downsides turn into benefits, but that's when solar hot water works even better than the heat pump water heater.

 

[Ampster]

Do they ever put these things on sale ?

I found one at a local plumbing supply house at a much better price than HD.

 

[Ampster]

I don't see how these things are of any benefit at all in the winter.

I get the heat for mine from the attic. In the winter I can direct the cold exhaust to outdoors. It had a payback of less than three years compared to a resistance element water heater. It may depend more on the local electrical rates rather than the weather. The lower the electrical rates the longer the payback.

 

[SkyBlue]

I don't see how these things are of any benefit at all in the winter.

My 50 gallon GE Geospring heats our water year round on heat pump alone here in Northern California. It takes half an hour to heat the tank in the summer and one hour + in the winter, drawing 625 watts/hour. It does drop the temperature in the garage by a degree or two, but as Tigerwillow wrote, that's a real plus in the summer. Unfortunately, GE stopped making hybrid water heaters years ago and there are only a few other manufactures still selling them.

 

[Ampster]

GE stopped making hybrid water heaters years ago and there are only a few other manufactures still selling them.

My GeoSpring gave up after only five years and I have since only used Rheem or Ruud which are the same and have proven to be quality.
As far as the temperature drop after several showers, my solution is to turn up the temperature to 135 degrees and use a tempering valve which increases the effective quantity of hot water.

 

[BMcL]

Here's two good ideas :
To quieten the loud compressor, make a surrounding box lined with cheap towels

And if you don't have a floor drain nearby, one previous poster mentioned putting a 5 gallon bucket under the condensation pipe.
Great idea !

 

[jsmetalcraft]

I just found out about these hybrids. I looked up my current heater and it's 20 yrs old, so I assume in short order it's time for a new one.

Talking to a friend who has a hybrid. He said he really did not notice a great savings on his power bill.

My current element heater says average yearly is $394. Hybrid is $105. 4.5 year pay back with $300 Fed tax credit and $300 power company rebate. Sounds good on paper.

Been monitoring the heater power usage. Been averaging less then 5kwh/day. So that comes to $150 a year. The noise issue concerns me. I have a basement. If set up right one could vent out in winter and in during the summer. Either way the ground will absorb or radiate a constant 67 degrees in theory ( I think I see swings of 68 in Aug and 62 Jan.). Just don't know, think , or determine if there is much saving other then the peak watts used each time the elements turn on, 5k vs 700.

My elements come on every four hours for 15 minutes or 3.75 minutes every hour for maintenance. Obviously I see the spike each morning when one shower is taken. Based on power usage can I assume that the hybrid would come on the same amount of time but using 25% less power? Or what is the run time of each cycle when just maintaining the temp?

 

[Ampster]

Talking to a friend who has a hybrid. He said he really did not notice a great savings on his power bill.

My current element heater says average yearly is $394. Hybrid is $105. 4.5 year pay back with $300 Fed tax credit and $300 power company rebate. Sounds good on paper.

My experience is the same as you posted. The EPA tags are based on $0.12 per kWh average rate in USA. My lowest rate in California is $0.20 per kWh. When I did the math at my rate the savings were even greater.

Your friends experience seems anectdotal. I prefer quatitative analysis instead of adjectives and adverbs when doing ROI calculations.

 

[Ampster]

what is the run time of each cycle when just maintaining the temp?

Good question. I have not figured that out. I can add that I believe the hybrids are better insulated than a resistance based WH so, as I said earlier using kWhs over the same usage period would be the best measure. Also I sometimes travel for weeks at a time and being able to remotely put the WH in vacation mode can save you money. The remote feature is great because I often forget some of those setback tasks when leaving for a vacation,

 

[jsmetalcraft]

My experience is the same as you posted. The EPA tags are based on $0.12 per kWh average rate in USA. My lowest rate in California is $0.20 per kWh. When I did the math at my rate the savings were even greater.

The resistive heater's tag was from 1994 and based on .08/kwh. Very close to what I pay (ave .086). I din't see what price the $105/ year is based on. If it is .12/ kwh then it makes my numbers better. Have to look it up. BTW in summer over 800kwh/ month my cost is just below .12/kwh.

 

[efficientPV]

averaging less then .5kwh/day.

That is a really low value. I am low use and my figure is about 2KWH a day with a heat pump. At camp it is about 2.5KWH with resistive solar. 1KWH is about the minimum heat loss a day for even efficient tanks. I figured over a 4 month period in winter I saved $.47 a day with my HPWH.

 

[Brett V]

I've had a Geospring in service for about 8 years now, still going strong. At the time I bought it, it qualified for a 30% Federal tax incentive and my local power company was pitching in a $200 rebate.

 

[efficientPV]

I paid $320 for a new NYLE shipped (no rebates) and even at that it barely pays for itself. Biggest plus is it dehumidifies the basement. Too bad that NYLE doesn't make consumer external HPWH anymore.

 

[BruceM]

The energy efficiency is going to depend on the incoming air temperature, and whether you are increasing your space heating bill in the winter.
I live off grid. II recently put together a DIY water chiller for my in floor heat system, with a new 12000 BTU compressor/condenser unit taken from a new LG window unit. SInce I could measure water temperature at the 2 GPM flow rate, I could easily see BTUs and Watts. I could get a COP of 5 at air temps (n the shade, measured at air inlet) at or below 82F with the expansion valve adjusted for full power operation, but above that the COP (watts out over watts in) dropped fast to 2. So I found to get the cooling I needed at an acceptable to me (1500W max) power level, an evaporative pre-cooler was needed to allow middle of the summer day temperatures. I also found that in full sun, air temperature near the ground was 10 degrees hotter than air temperature at 6 foot height, so I need to add an insulated vertical intake duct.

I think we should all be thinking about ground source whenever we consider heat pumps/refrigeration, if we are interested in conserving energy. With ground source for space and domestic water heating, and kitchen refrigerator/freezers, a great deal of energy can be saved as all year round the COP can be 5 or better. The costs of installing ground source systems must be addressed- somehow.

Heating your home domestic water in winter by chilling the air near the heater tank is pretty nutty when the house needs heat, not chilling.
The energy estimates are likely based on average water heater room temperatures which you may not be able to maintain in winter.

 

[Ampster]

. The costs of installing ground source systems must be addressed- somehow.

I agree but some locations do not have enough real estate or the real estate would be too expensive to dig up so the next best thing would be air source.

 

[RCinFLA]

Approximate numbers for a typical hybrid heat pump hot water heater is it moves 3000 to 4200 BTU'/s per hour for about 500 watts of electric power consumption.

A conventional heating element produces about 90% of 3400 btu's per 1000 watts of electric. That is 3060 btu's/hr per kWH.

Just with these two benchmarks, a hybrid is about 2.5 more efficient.

The down side is imagining living with a conventional hot water heater that only has a 1000 -1200 watt conventional heating element. This represents the water temp recovery rate the hybrid will achieve running solely on heat pump.

Most conventional hot water heaters have 3kW to 4 kW heating elements and a top and bottom element of this wattage (they both don't activate at same time). Top element only activates when tank is depleted of most of its heated water so top will heat up water quicker for immediate demand delivery which is taken from top of tank.

------------------------------------------------
From GE hybrid hot water heater spec sheets, its 50 gallon unit can recover 8 gallons per hour solely using heat pump with ambient temp of 68 degs F and heated hot water to 120 degs F with a heat pump running 550 watts of electric power.

Average shower is 6 to 10 gallons of 120 deg water, mixed with cold water to get desired shower temp. So you can see there might be a recovery time issue if you have several people taking showers around the same time.

From the 8 gallons of reheating data, this translates to a BTU/hour generation of 3,328 BTU's/hour rate, consuming 550 watt-hours.

A 4500 watt electric element generates 15,365 BTU's per hour, consuming 4500 watt-hours.

So, heat pump recovery is about 4.5 times slower than an electric element.

Heat pump yields 6.05 BTU's per watt-hour.
Electric resistive heating element yields about 90% of 3.414 BTU's = 3.07 BTU's per watt-hour.

Heat pump efficiency factor would be 6.05/3.07 = 2.0 over conventional electric heating elements .

Heat pump hot water heater manufacturers claim 1.5 to 2.5 for EF. 1.5 would likely be using some electric heating element recovery assist. Numbers greater then 2 are using only heat pump and their improved tank insulation over a typical electric element hot water heater, by as much as 20% less tank heat loss. They put more insulation on hybrid heat pump units. They work best above 80 degs F environment and almost produce nothing if ambient temp is below 40 degs F.

 

[sunshine]

The costs of installing ground source systems must be addressed- somehow.

Been around for sometime. I often think we have our modern multistory buildings upside down. We use the best floors for the car park..and we call cavemen stupid! Not much money in passive solutions probably the biggest hurdle.
Heat pump technology may be great if we compare that to other methods of climate control but I can not get past the fact that by only looking at direct efficiency, watt vs watt, we mislead ourselves to the true costs.

 

[BruceM]

I agree, efficiency (and performance if limited to 500W) is seriously limited at cold ambient air. Thanks for the details and thoughtful analysis.
Florida might be a great place for these, for those that can learn to live with the slow recovery.

I live off grid at 5600 ft in central eastern AZ. Moderate winters with some snow, plenty of single digit F nights. I went with a homebuilt 4x32ft horizontal riser aluminum over copper flat plate solar water heater, which drains back to an homebuilt 800 gallon insulated tank. With copper pipe coils for domestic HW and in floor heat, it solves my hot water issues as well as space heating via in floor heat. Propane backup Dec-Feb. It has served me well, for my small 1100SF, super insulated (Canadian style double wall) home.

My interest in this thread is because I like to think about the future of off grid home design- without propane. Heat pumps with ground source seem very appealing for that. After my experience this last summer experimenting with a 12000 BTU water chiller, I'm now newly skeptical about efficiency claims on refrigeration/heat pumps (air exchange). They hide the real performance in the new seasonal average performance data.

Well bores filled with 1" PEX (closed) loop are popular for ground source, and require little space, but are damned expensive. I've got sandstone at about 5 food deep so dug trenches aren't viable. 65F all year round at about 10-12 foot deep (confirmed), but not cheap to get to. It would be a great temperature for direct winter greenhouse heating (in foor for large surface area), heat pump, water chiller.

 

[Brett V]

Geothermal heat pump systems have always fascinated me. I know almost nothing about them except a guy I used to work with had one put in. He said it was very expensive and commented once about questioning how efficient it would be when the installer said they needed a spot to install a 40 amp breaker in his panel.

 

[Ampster]

He said it was very expensive and commented once about questioning how efficient it would be when the installer said they needed a spot to install a 40 amp breaker in his panel.

That is one opinion. When I installed a HPWH an old school plumber said it would never work well in Northern California. My opinion after installing three of them for me and friends is that they saved money and are three times more efficient than electric element water heaters. California has high energy costs so the payback has been very good. Mine only draws 10 Amps at the most, when in heat pump mode.