The Winter Space and Water Heating Challenge
The most significant challenge for a true ZEH in cold cloudy climates is space and water heating during the winter months. Passive solar and active solar heating options require the sun. The cloudiest months are the winter months of November, December and January which on average have about half as much sun as the summer months. For example in Grand Rapids, Michigan, December’s sunshine is 37% of that of July. Portions of the cold and cloudy northern tier can occasionally have winter months with less than 25 hours of sunshine. Thus, another heating renewable heating source is required.
There are basically two options, storage of renewable heat source or storage of renewable kilowatt hours. Heat sources can be stored as wood (i.e., any biomass) for combustion in stoves. Some ZEH designs have stored renewable heat in large thermal mass, such as the ground (Drakes Landing), water, phase change material. Solar thermal storage in large thermal mass is not a fully commercialized strategy.
For utility grid-connected homes, the storage of renewable kilowatt hours is best done using a renewable electric generation technology, solar or wind, and a retail net energy billing rate (if available). With a net energy billing rates excess production, during windy or sunny portions of the year, can be ‘stored’ on the utility grid until it is needed. For example a properly sized, net energy billing solar electric system would over produce in the summer and under produce in the winter. While a wind turbine would tend to over produce in the spring and fall and under produce in the summer.
The most efficient means of electric heating in cold and cloudy climate are ground source heat pumps (GSHP) for space heating and air source heat pumps for water heating. GSHP can produce hot water, using a desuperheater, but we have not found any successful applications.
Passive and active solar heating system should also be used in a ZEH to reduce the annual heating load on heat pump systems (and thereby kWh consumption).
ZEH designers have consider combining large thermal storage system with heat pumps. But we are not aware of any such operational systems. GSHP that provides space cooling in the summer will increase the temperature of the ground (i.e., thermal storage) – increasing heat pump efficiency in the early winter. However heat losses to the surrounding ground are very high.
Our conclusion is that about the only mainstream option for renewable water and space heating are ground source heat pumps coupled with solar electric or wind turbines.
There are basically two options, storage of renewable heat source or storage of renewable kilowatt hours. Heat sources can be stored as wood (i.e., any biomass) for combustion in stoves. Some ZEH designs have stored renewable heat in large thermal mass, such as the ground (Drakes Landing), water, phase change material. Solar thermal storage in large thermal mass is not a fully commercialized strategy.
For utility grid-connected homes, the storage of renewable kilowatt hours is best done using a renewable electric generation technology, solar or wind, and a retail net energy billing rate (if available). With a net energy billing rates excess production, during windy or sunny portions of the year, can be ‘stored’ on the utility grid until it is needed. For example a properly sized, net energy billing solar electric system would over produce in the summer and under produce in the winter. While a wind turbine would tend to over produce in the spring and fall and under produce in the summer.
The most efficient means of electric heating in cold and cloudy climate are ground source heat pumps (GSHP) for space heating and air source heat pumps for water heating. GSHP can produce hot water, using a desuperheater, but we have not found any successful applications.
Passive and active solar heating system should also be used in a ZEH to reduce the annual heating load on heat pump systems (and thereby kWh consumption).
ZEH designers have consider combining large thermal storage system with heat pumps. But we are not aware of any such operational systems. GSHP that provides space cooling in the summer will increase the temperature of the ground (i.e., thermal storage) – increasing heat pump efficiency in the early winter. However heat losses to the surrounding ground are very high.
Our conclusion is that about the only mainstream option for renewable water and space heating are ground source heat pumps coupled with solar electric or wind turbines.
posted by niels at 12:31 PM
0 Comments:
Post a Comment
<< Home