Quick Answer
To size a solar hot water system for a family, calculate the household's daily hot water demand and choose a system that meets this need, typically around 80-100 gallons per day for a 4-person household.
Calculating Daily Hot Water Demand
To estimate daily hot water demand, consider the number of occupants, their shower habits, and other water-using appliances. A good rule of thumb is to allow 20-30 gallons per person per day for showers and baths, plus additional gallons for washing dishes, laundry, and other uses. For a 4-person household, this translates to 80-120 gallons per day.
Selecting a Solar Hot Water System
When selecting a solar hot water system, consider the type of collector: flat plate, evacuated tube, or concentrating. Flat plate collectors are suitable for most applications, while evacuated tubes perform better in colder climates. Concentrating collectors are more expensive but offer the highest efficiency. A 4-person household typically requires a system with 4-6 collectors, each with 2-3 square meters of collector area.
System Sizing Considerations
In addition to the number of collectors, consider the system’s thermal storage capacity, typically measured in gallons or liters. A 100-gallon tank provides a good balance between storage and cost. The system’s pump and piping should be sized to ensure efficient water circulation and minimize energy losses. A well-insulated tank and piping system will also help minimize heat losses.
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