I am modelling a passive house and want to get the temperature ranges for each zone between 16 and 25 C. I have a HVAC systeme with heat exchanger for winter and then the heat exchanger is turned off in summer. However the the heat exchanger is turned off there is a rapid drop in temperature and then the spring and autumn months are either too hot or two cold with fuctuations between these. Is there a way of reducing the gradient of temperature change between the heat exchanger being on and off?