Operational strategies for attached sunspaces in Canada

Abstract

Sunspaces are gaining considerable consumer appeal and acceptance, however, very little quantitative information exists in terms of their thermal performance in occupied houses. A major concern in the year round use of sunspaces is the control of the air temperature. This problem is usually dealt with in the design stage through proper selection of window areas and envelope thermal properties. However, even a well designed sunspace can have temperatures that fluctuate outside the thermal comfort zone for a significant portion of the year. During this time, auxiliary energy for both heating and cooling must be provided if the sunspace temperature is to remain in the comfort zone. A mathematical model that can accurately predict the thermal performance of a sunspace is required if the auxiliary energy requirements are to be examined over a range of operating strategies and under typical meteorological conditions.

The sunspace model developed consists of finite difference approximations of all the major surfaces such as walls and ceilings. Heat transfer through the doors and windows and infiltration are included in the model as paths directly between the outside or house and the sunspace. Auxiliary energy, in the form of heating and air conditioning, and natural cooling has also been included in the model. Four sunspaces located in Saskatoon, Saskatchewan are examined to verify the model.

Yearly simulations using Typical Meteorological Year weather data are performed on all the sunspaces to determine the auxiliary energy requirements under different strategies. These yearly simulations are extended to three other cities representative of the major climatic regions of Canada. From these simulations, operational strategies on the use of auxiliary energy for attached sunspaces are developed.

Of the four sunspaces investigated only one has the potential to become a net producer of energy. However, reductions in the yearly auxiliary energy requirements of the sunspace of up to 80% are possible when proper operating strategies are implemented. Effective operating strategies should include,

• the shutting down of the sunspace from December to February to reduce the heating load of the sunspace,

• venting any useful energy produced by the sunspace during the winter to the house for space heating, and,

•using a exhaust fan to the outside to reduce the air-conditioning requirements of the sunspace.