In my reports on annual figures for the PV system, I always analyzed the largest consumers in the house. We have now been living in a plus-energy house for more than a year and produce more energy than we need throughout the year. In all the analyses, I always came to the conclusion that the next major measure for us must be to replace the classic hot water boiler with a domestic hot water heat pump, or BWWP for short. This was finally implemented on June 1st and we now have initial empirical values after a month with WP-Boiler.
WP boiler freshly installed in the basement
Why WP boiler?
I already have a 20-year-old heat pump for heating. Unfortunately, the previous hot water boiler is spatially completely in another corner of the house and so a combination of both with a heat pump would have required enormous structural measures. Accordingly, the decision was clear and simple, I use a WP boiler for hot water heating. These are very efficient and can work directly with the ambient air in the basement. The basement must be of the right size, but then that’s not a problem. A nice side effect is that it also dries the basement and is therefore also ideal for laundry.
A 300L WP boiler installed for the family of 4
Natural Refrigerant (R290)
A much-discussed topic is the PFAS – “forever chemicals”. Conventional WP boilers have such hard-to-degrade chemicals in them. When evaluating the hot water heat pump, I made sure that it also uses a natural refrigerant. Propane (C3H8) is one of them (hydrocarbon) and is also known in refrigeration technology under the designation R290 – R290 is PFAS-free. Propane has neither an ozone depletion potential (ODP = 0) nor a significant direct greenhouse effect (GWP = 3). Thanks to its excellent thermodynamic properties, propane is a particularly energy-saving refrigerant. Further information on refrigerants for heat pumps and air conditioning units can also be found in the instructions from the Federal Office for the Environment (FOEN).
The Phnix airExpert R290 uses a natural refrigerant
Choice of boiler and recommendation
I chose the Phnix airExpert R290, also mainly on the recommendation of a colleague in the industry. In some tests, this heat pump has particularly impressed with its energy efficiency and very low noise emissions. Especially for us with the office next to the basement room with the HP boiler, this was a decisive argument for choosing a very quiet unit. Even after a month of use, I can only confirm that the airExpert is convincing in this regard.
Project WP boiler implemented
Thermosiphon
Of course I got advice before the installation and had the installation carried out by a specialist from Haustechnik Oppliger. So I can finally enjoy a thermosiphon. This is connected directly to the hot water outlet of the heat pump and prevents convection. In simple terms, this means that with a connection without a thermosiphon, the warm water rises and cools down on the pipe wall of the connected pipe. The cool water (because it is heavier) descends again along the pipe wall and cools the storage tank. This effect is prevented by the thermosiphon and thus of course increases the system efficiency through reduced losses.
Thermosiphon is part of a good installation
Isolation
Unfortunately, our hot water pipes were not insulated. In the course of all the conversion work, we also did this right away and also had the hot water pipes insulated up to the riser zones. On the one hand, of course, this also looks much better, but I also hope that there will be a gain here due to lower heat losses. Mainly because these pipes transport water with temperatures of >50°, not with low flow temperatures as in our HP. The losses should thus be reduced, but unfortunately this is hardly measurable.
Thermosiphon insulated Hot water pipes insulated
Savings of >70%
Since I monitor and measure everything as usual, I have been collecting electrical consumption data for my hot water generation since 2017. I have now compared the last few years with the classic heating element with the needs of the new BWWP.
Energy comparison HP boiler in June
On average, I needed around 190 kWh of electrical energy in June and just 55 kWh this June. This corresponds to a saving of 71% (!!!), or an efficiency factor of 3.5. These are great values and of course I will monitor them throughout the year and will be happy to report back.
Massive savings for hot water treatment by BWWP
Conclusion
I am absolutely thrilled with the efficiency of the WP boiler and am currently saving massive amounts of electrical energy for hot water preparation. A saving of over 70% is enormous and, according to my projections, reduces our annual electricity consumption by a whopping 1,600 kWh. With this saving, I can cover around 9000 km with my electric car, cool right? This will certainly be reflected in my self-sufficiency of the plus-energy house and increase it again. In addition, this will also make itself felt financially, in the spring to autumn I will feed in significantly more PV electricity and reduce the grid purchase in winter. I will definitely report back on this, also with regard to the connection to the PV system and app…
I got the Phnix airExpert R290 heat pump boiler from Renewconsult and it costs around CHF 5000 with installation.