Several of our Thousand Home Challenge projects and candidates are using ductless heat pumps for space heating and cooling. I will be posting data addressing hot weather performance and invite you to participate in this discussion.
ACI conducted 2 webinars addressing Ductless Heat Pump this past May, sponsored by Pacific Gas & Electric's Energy Training Center. The data and experience of the presenters, Bob Davis, Mark Jerome, and Marc Rosenbaum focused on space heating. The PowerPoint presentations, audio, and resources from these webinars is posted on the Thousand Home Challenge website. Here is the link: http://thousandhomechallenge.com/thc-webinars-ductless-heat-pumps.
In Ward Lutz's home his 9RLS Fujitsu ductless heat pump used 2-3 kWh/day for cooling, running continuously with outside temperatures frequently above 90 degrees.
We have had some pretty nasty heat and humidity this past month in much of Eastern US. Here is data from Ward Lutz’s Thousand Home Challenge home in Urbana, Ohio that uses a RLS9 Fujitsu DHP with the outside coil installed in the isolated crawl space. (It is an experiment – crawl space ceiling is insulated to R 40 and Ward closely monitors crawl space temperature winter and summer). Ward’s house is a one story small frame home (~575 square feet) that he superinsulated several years ago. Here is the link to his THC case study (http://thousandhomechallenge.com/case-studies). The case study has not been updated with the most recent energy use yet – with a 2.5 KW PV array he is now net zero.
The three attached spreadsheets include manual temperature and humidity readings (interior, exterior, crawl space) taken over two different time periods. The ductless heat pump is submetered. Energy use (kWh) for the house and the DHP, as well as and PV output is summarized (1st doc). Part of the cooling load is internal gains, particularly a problem in a very small well insulated house – even with a low baseload. The third spreadsheet includes analysis and a graph by Bill Rose examining the vapor pressure in the crawl space, house, and outside.
Do you have ductless heat pump hot weather data to share? Any thoughts on how the house would have performed differently in a drier climate? Any thoughts (or data) on achieving comfort/distribution of cooling in a larger house?
Below is an e-mail from Danny Parker, Florida Solar Energy Center. Danny is a Thousand Home Challenge candidate. - The embedded graphs do not appear to function in this discussion. Check the attachment for data. I will follow-up with the graphs.
Hi Linda and others,
I also have a Fujitsu 9RLS in my 2060 square foot home in Cocoa Beach, Florida. Slab on grade home with R-19 in the ceiling with a white roof, R6 EIFS insulation on the outside of the concrete block walls, advanced windows (U=0.29, SHGC= 0.24) and lots of efficient appliances inside.
The home is heavily instrument by the Florida Solar Energy Center for U.S. DOE and we ran an experiment this summer using the Fujitsu to cool the entire home compared with using the 2-ton SEER 10 AC with the attic duct system (which was sealed). Central system was used for a one week period.
All data is on-line here:
Here are two plots of the data from June 15th - July 15th while the home was occupied (we're on vacation now). I've also attached the data for the period as an Excel sheet.
Here is the power data. No need to describe when the central AC is used (red is the outdoor condenser; green is the air handler fan; blue is the mini-split). Note from the second plot how the central system does not result in lower relative humidities-- higher actually. That's not surprising since the single-return central system depressurizes many rooms in the house during operation, while the mini-split does not. About two degrees lower was maintained in the home in the last week with the mini-split than during the rest of the time.
HOBOs are in each room recording that variation of temperature which I plan to report at a later point (the entire write up on this experiment and the history of retrofits in the home is awaiting approval as an NREL report being issued to DOE).
Hoping this adds to the discussion.
The same period with the interior main zone and central hallway temperatures and relative humidities:
Check out this attachment for Danny Parker's graphs -( ductless heat pump vs central AC in a 2000 square foot home in Florida) referred to in the second reply.
I just spent some time at the website where his household energy and weather data from December 2010 to the present is available for reviewing and filtering. Great resource!
We have updated info from Ward Lutz's hot weather ductless heat pump performance - as well as more recent information on his home's energy use, production, and success at dropping radon levels significantly. Check out the nonconventional approach to control radon @.1 kWh/day, and the non-traditional approach to his crawl space.
From June 20 to July 9, 2012 there were 11 days when the temperature was above 95 degrees outside of
Ward Lutz's small home in Urbana, OH.
During that 20 day period, Ward's submetered minisplit (9 RLS Fujitsu) energy use was 41.5 kWh, averaging
less than 2.1 kWh/day.
For much of that period his thermostat set-point was 78 degrees F. During the 4-day period when the
thermostat was set on 74 degrees F his daily DHP use averaged 4.7 kWh.
Here is the link to a presentation from July of this year.
Here is the link to the Ward Lutz, Ohio NZE retrofit project referenced in this discussion.