Can I see details about the heating and domestic hot water systems of the Edelweiss house?
August WehrmannMarch 10, 2019Last updated: Aug. 3, 2020
I saw the article on the CaGBC site regarding the Edelweiss house where it indicated "a hydronic radiant floor and an air source heat pump". Can you post more details on which systems were used? For example, is the ASHP being used to heat the fluid in the radiant flooring? If not, what system was used for that? Also, what system was used for domestic hot water?
Thanks
Responses (3)
Emmanuel CosgroveMarch 19, 2019, 5:41 p.m.
The radiant floor is heated with an electric boiler, it is a separate system than the heat pump. The intention of the heated floor is primary to ensure comfort and happy feet, the air-source heat pump is far more efficient and so we rely primarily on that to heat the air of the home.
The domestic hot water is a heat pump as well, we used an AO Smith air-to-water hybrid heat pump. The water heater sucks in the air from the home (which with the heat pump is generated more efficiently and affordably than by the floor) and so it in turn transfers that ‘efficiency’ to the water heater.
An even greater benefit is in the summer months as the water heater in effect acts to cool the air in the house, so much so that most summers the air-source heat pump is actually never operated for cooling.
A greater explanation can be found on the following pages
I see the air-to-water heat pump solution being promoted quite often in net zero homes. It has been noted that this is a detriment in areas dominated by heating. Since it takes heat from the air, it creates additional load on the primary space heating system. In net zero designs, if an air source heat pump is used for space heating and an indoor air to water heat pump is used for DHW heating, the net efficiency of the DHW heat pump is less than 100%. If both heat pumps have seasonal COPs of 3.0 during the heating season, then the DHW heat pump has an effective COP of only 1.8. If the DHW heat pumps seasonal COP is closer to 2, then its effective COP drops to 1.5. For the added expense of an indoor air to water DHW heater, only getting 50% more efficient than an electric water heater is a very long payback. A better solution is to use an air to water heat pump that can serve both DHW and space heating loads using outdoor air. These can be combined with electric backup for the coldest days and augmented by solar thermal to be really efficient year round. (James Bererton, P. Eng., Eta Energy Solutions)
In our case the primary heating system of this house is the sun, since over 50% of the heat load is provided by passive solar heating. Therefore, a portion of the domestic hot water is also effectively solar heated. And due to the shading, extreme insulation and airtight envelope, the cooling needs are also dramatically lower than a code-built house, so the cooling provided by the heat pump water heater as it extracted heat from the air was all that was needed to keep the home comfortable in the summer months. That means no additional cost for cooling, and also no additional wear on cooling equipment.
You make a good argument, but all cases are different and there are often additional spin off benefits like the above. That said, we would not put a blanket recommendation on this heating strategy in every climate, with every grid power source, or with every home design. Conversely, we would not put a blanket dismissal on it either, since in a case such as this there are tangible benefits both financially and from an ecological stand point as well. Thanks for sharing your thoughts James.
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The radiant floor is heated with an electric boiler, it is a separate system than the heat pump. The intention of the heated floor is primary to ensure comfort and happy feet, the air-source heat pump is far more efficient and so we rely primarily on that to heat the air of the home.
The domestic hot water is a heat pump as well, we used an AO Smith air-to-water hybrid heat pump. The water heater sucks in the air from the home (which with the heat pump is generated more efficiently and affordably than by the floor) and so it in turn transfers that ‘efficiency’ to the water heater.
An even greater benefit is in the summer months as the water heater in effect acts to cool the air in the house, so much so that most summers the air-source heat pump is actually never operated for cooling.
A greater explanation can be found on the following pages
In our case the primary heating system of this house is the sun, since over 50% of the heat load is provided by passive solar heating. Therefore, a portion of the domestic hot water is also effectively solar heated. And due to the shading, extreme insulation and airtight envelope, the cooling needs are also dramatically lower than a code-built house, so the cooling provided by the heat pump water heater as it extracted heat from the air was all that was needed to keep the home comfortable in the summer months. That means no additional cost for cooling, and also no additional wear on cooling equipment.
You make a good argument, but all cases are different and there are often additional spin off benefits like the above. That said, we would not put a blanket recommendation on this heating strategy in every climate, with every grid power source, or with every home design. Conversely, we would not put a blanket dismissal on it either, since in a case such as this there are tangible benefits both financially and from an ecological stand point as well. Thanks for sharing your thoughts James.