22 May 2008

SYSTEM PERFORMANCE OF HVAC IN A LOW ENERGY HOUSE IN THE COLD REGION OF JAPAN


This study describes a field test on a low energy house built in the cold region of
Japan. The floor area is about 200 m2. The building envelope consists of high insulated walls
and windows and a floor with high heat capacity. Totally the Q-value and C-value are 0.96
W/(m2·K) and 0.4 cm2/m2 respectively.
For heating and cooling, a ground source heat pump unit made in Japan is installed.
Continuous heating operation indicates that the supply temperature for floor heating can be
mostly kept low between 30ºC and 35ºC throughout the season. The daily average heating
output is 3.0 kW, where higher COP can be achieved due to the partial load operation. We
can also observe a high seasonal performance. The system COP including the pumping
power reaches 4.45. Besides it, acceptable thermal environment is brought about at an air
changing rate of 0.5 hr-1. The room temperature is kept stable above 20ºC all day. The
vertical temperatures also show uniform distributions.
From the monthly electric consumption, the largest consumption is showed in January due
to the heating operation. The power production by the solar photovoltaic (PV) system nearly
reaches the consumption in the summer season. The total amount of the annual electric
consumption consists of 37% of heating, 10% of DHW and 53% of ventilation, lighting and
the rest. The real consumption, that is, the difference between the production and
consumption, is observed at 24 kWh/m2, which is equivalent to 236 MJ/m2 in the primary
energy amount. Totally 48% of the electric power demand can be covered by the PV system.