The classic way of estimating heating load in smaller, envelope-dominated buildings is to assume the rate of heat loss is proportional to the difference between the inside and outside temperature.
In last month’s column, I presented a “template” for a system that provides space heating, cooling and domestic water heating using a cold climate air-to-water heat pump as the primary heat source, and the sole source of chilled water for cooling.
Most hydronic heating systems that have renewable energy heat sources, such as solar thermal collectors, an air-to-water or geothermal heat pump or a biomass boiler also have an auxiliary heat source.