Quick Answer
To determine the right size for a solar thermal system, calculate the total energy demand, considering the building's insulation, climate, and heating requirements. Use the Solar Heating and Cooling (SHC) system sizing guidelines or consult with a professional to ensure accurate calculations. Consider the system's efficiency and the desired backup heat source.
Assessing Building Energy Demand
To size a solar thermal system for radiant floor heating, begin by calculating the building’s energy demand using the “Degree Day” method. This involves estimating the building’s heat loss in terms of heating degree days (HDD). For a typical US climate, assume 7,200 HDD per year. Next, estimate the building’s heat loss in Watts using the formula: Watts = 1000 * HDD * 24, where HDD is the heating degree days per day. For example, a 2,000 sq. ft. house with 30% glazing in a moderate climate might require 8,000-12,000 Watts of heat.
System Sizing Guidelines
Consult the Solar Heating and Cooling (SHC) system sizing guidelines, which provide a comprehensive framework for sizing solar thermal systems. According to the SHC guidelines, a general rule of thumb for sizing a solar thermal system is to provide 50-70% of the building’s total heating demand. For radiant floor heating, this might translate to a system size of 10-14 m² (108-151 sq. ft.) of collector area for every 1,000 sq. ft. of building area.
Efficiency and Backup Heat Source
When sizing a solar thermal system, consider its efficiency and the desired backup heat source. A well-insulated building with a high-efficiency solar thermal system and a reliable backup heat source can reduce the system size and cost. For example, a system with a 0.8 efficiency rating and a 90% efficient backup heat source might be sized 10-20% smaller than a system with a 0.6 efficiency rating and a less efficient backup heat source.
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