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Field Test Best Practices: A Resource for Practical Residential Building Science

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Precipitation can affect the performance of a house and some specific systems. For example, if a large amount of rain falls, the soil conductivity will change, which will affect the performance of a ground source heat pump. Rain wets the house envelope assembly, and the assembly needs to be properly designed to withstand frequent wetting and drying cycles. A layer of snow can insulate the roof and increase the reflectance of the ground. While precipitation can affect a number of systems in or around the outside of a home, it is not a commonly monitored quantity for field tests. However, if the effect of precipitation on specific system (for example: rain water harvesting systems) was a focus of a particular field test, it would be appropriate to install precipitation sensors.

Note: A typical sensor for measuring the rate of rain fall, a tipping bucket rain gauge, is more commonly used to measure condensate flow rate. Even though using the tipping bucket for its intended use may not commonly be done in a field test, the sensor is still useful for buildings research.

Tipping Bucket Rain Gauge

A common sensor for measuring rain or condensate is a tipping bucket rain gauge. Rain is collected in a funnel on the top of the assembly and is directed into the "tipping bucket." The tipping bucket is shaped like a roof truss, with a fulcrum in the middle like a seesaw. The truss will tip when a preset amount of water is collected on one side and the other side will begin filling. This action will trip a reed switch sending a pulse to the data logger. Since the volume held in the bucket is known, the rate of pulses is used to determine the rate of rain falling or the rate of condensate production. This method works well for low flow rates and becomes less accurate for higher flow rates. As one example, the tipping bucket rain gauge made by Texas Electronics does not accurately capture flow rates higher than 1.5 liters/hour.