All, one more post on HPWH from one of favorite organizations: Green Building Advisor
https://www.greenbuildingadvisor.com/question/how-to-calculate-power-consumption-for-heat-pump-water-heater
Their articles are extremely well researched and written, and their Q&A postings are well monitored and reviewed.
Original Message:
Sent: 07-29-2024 03:48 PM
From: william fitch
Subject: Read our innovation-showcase issue of Solar Today
Occom's razor works on that idea, but, its all in how you verbally phrase the two options. One PV panel is not going to provide enough electrons to handle, lets say a family of 4, DHW load. A single 350W panel will yield about 420 or so KWH's a year. A typical DHW load for 4 will be about 2,200KWH's a year. So one panel will not even cover one person.
AS far as extra insulation goes, you don't need PV for that savings, or electric water heater timers, depending on occupant schedules, can hep reduce load.
So if you really want a PV offset, better use an extra 5 - 6 panels, room provided.
Regarding resiliency, the more you integrate the less you have.
Always choices.....
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william fitch
Owner
www.WeAreSolar.com
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Original Message:
Sent: 07-29-2024 10:35 AM
From: Steve Kawell
Subject: Read our innovation-showcase issue of Solar Today
I have a little different take on what is the best way to generate cost effective domestic hot water.
Solar thermal systems work well but have high initial installation costs and high potential for maintenance.
Heat pumps work well in certain climates and locations.
They show good performance when located in the garage of a house in a warm climate but can be an energy drain if located in a conditioned space during the winter in a heating climate.
Many homes have or are planning to install a PV system, add an extra panel to the array and use a well insulated electric hot water tank on a timer set for daytime water heating.
Super simple and low maintenance.
It sure seems reasonable to just use electrons, less physical apparatus to deal with and maintain.
Steve Kawell
Durango, CO. 81301
970-769-3904
Original Message:
Sent: 7/28/2024 10:57:00 AM
From: M Keith Sharp
Subject: RE: Read our innovation-showcase issue of Solar Today
Below is a link to a study that quantified the savings for a HPWH. The study was done in Canada, so the ratio of heating to cooling loads is greater than for southern US states. But it shows the hidden cost of HPWHs when they increase heating loads during the winter. Compared to a conventional electric water heater in a family home, the HPWH saves $791 for heating water and $81 for space cooling in the summer, but costs $487 in extra space heating during the winter. Overall, the savings are about half of that calculated from the more efficient heating of water alone.
https://sustainabletechnologies.ca/app/uploads/2017/11/ASHPWH_Tech-Brief2.pdf
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M Keith Sharp
Emeritus Professor
Louisville KY
Original Message:
Sent: 07-25-2024 01:24 PM
From: M Keith Sharp
Subject: Read our innovation-showcase issue of Solar Today
In response to a question:
Solar water heaters produce around 50 times more heat than the electricity used to power pumps and controllers. A heat pump water heater (HPWH) produces 2-3 times more heat than the electricity used to power its compressor, but about half of that heat is taken from the air surrounding the HPWH. If the HPWH is in the conditioned space, then the space heater (furnace, heat pump, etc.) must come on to replace that heat during the heating season. During the cooling season, the cooling effect of the HPWH is beneficial. Trouble is, only a few climates in the US have cooling loads larger than heating loads. In most US climates, the HPWH works against space heating more often than it benefits cooling. In general, solar water heaters are roughly ten times more efficient to start with.
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M Keith Sharp
Emeritus Professor
Louisville KY
Original Message:
Sent: 07-22-2024 03:48 PM
From: Kat Friedrich
Subject: Read our innovation-showcase issue of Solar Today
Thanks for your comments!
Keith and Bill, I'll send Jim a comment via email about a potential correction and cc you.
Best regards,
Kat
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Kat Friedrich
Editor in Chief
American Solar Energy Society
Monona WI
Original Message:
Sent: 07-18-2024 09:06 PM
From: M Keith Sharp
Subject: Read our innovation-showcase issue of Solar Today
Agreed. With a heat pump water heater drawing heat from the house, the heat pump space heater would have to be used more. Solar thermal water heaters are better from an energy perspective than heat pump water heaters for all but a few of the hottest, southern locations, where the cooling in beneficial. See the NREL report below:
K. Hudon, T. Merrigan, J. Burch, J. Maguire, Low-cost solar water heating research and development roadmap, National Renewable Energy Laboratory, 2012. Technical Report NREL/TP-5500-54793 August, Low-Cost Solar Water Heating Research and Development Roadmap
| Osti | remove preview |
| | Low-Cost Solar Water Heating Research and Development Roadmap | | The U.S. Department of Energy's Office of Scientific and Technical Information | |
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Updated link. 21Jul24
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M Keith Sharp
Emeritus Professor
Louisville KY
Original Message:
Sent: 07-18-2024 04:03 PM
From: william fitch
Subject: Read our innovation-showcase issue of Solar Today
Yes. His location in CO, 7000 feet clear sky country is what jealousy is made of. 250 sunny days to my 176!. HDD at around 4000-5000 and CDD near 1000. New construction and super insulated is the way to go.
I would disagree with his thinking of, replacing the evacs for SDHW with PV. The COP for solar thermal is always way more then 50, unmatched by PV or heat pumps. The heat wasted comes at no economic or environmental cost. From a resiliency perspective as well, SDHW is greater, for the energy to pump, if not direct DC panel or thermosyphon, is next to nothing and easy to re-config in disaster situations.
The luxury of a new build. No constraints via existing structure. Yes, I am Jealous...lol....
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william fitch
Owner
www.WeAreSolar.com
Original Message:
Sent: 07-18-2024 01:32 PM
From: M Keith Sharp
Subject: Read our innovation-showcase issue of Solar Today
If you are thinking about building a house, or doing a remodel, the article by Jim Riggins is a must read. I am still amazed at the performance of the house and the quality of the design. It is nearly 100% heated and cooled by ambient energy. A heat pump was installed, but has rarely been used. Hot water is provided almost entirely by solar thermal collectors. Such a good example of how to minimize electrical demand. This is important, because the utilities are burning fossil fuels on our behalf, even if we are net zero.
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M Keith Sharp
Emeritus Professor
Louisville KY