HVAC systems in buildings consume the largest amounts of energy. They also contribute to green house gases significantly, and are responsible for ozone depletion. It has been shown that the best economically viable active solution for reducing the energy consumption from HVAC systems is the utilization of solar energy in buildings. In this study a combined solar space heating, cooling, and solar hot water scheme and methodology is proposed which will allow maximal utilization of solar thermal energy generated from solar thermal collectors, in all the seasons of the year. All calculations and assumptions have been done for the continental climate zones. An optimization objective function has been set up for determination of the optimum area of solar thermal collectors that could yield maximum cost savings, based on monthly energy consumption patterns. It has been shown that the suggested methodology provides full utilization of the available solar thermal energy, year round.