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

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Fluid Flow

A residential field test may require several different types of measurements related to fluid flow.  The most common is the volumetric flow rate of a liquid (often water or ethylene glycol) in a pipe, typically measured using a turbine flow meter. Air flow inside ducts and the flow entering or exiting a room are useful quantities for testing a variety of heating, ventilation, and air conditioning (HVAC) systems.  When natural gas consumption is of interest, gas meters are used to measure the volumetric flow rate of gas. Occasionally, there may be a need to measure the flow rate of steam or of a refrigerant, but these are more likely to be encountered in laboratory test settings, as are measurements of other characteristics of fluids, such as concentration and pressure. The options for measuring a variety of fluid flow rates in a residential setting are described in the following sections.

Liquid Flow

Measuring the volumetric flow rate of a liquid, usually water, is a common practice in field tests. Applications for measuring liquid flow include measuring whole house hot water use, hot and cold water use at individual fixtures throughout the house, and measuring the condensate generated by an air conditioner or heat pump.

Air Flow

There are a variety of ways to measure air flow rate in a field test setting. Unlike other fluid flow rate measurements of water or natural gas, air flow is not necessarily constrained to a pipe. Air flow rate in ducts is one place that air flow can be measured, but there are other places in the home that air flow rate may be desired, such as at the outlet of a vent. Some methods are more applicable in a short-term test situation, rather than a long-term installation. Collecting air flow rate measurements would be an important task when investigating the performance of heating, ventilation, and air conditioning (HVAC) equipment or when looking for duct leakage, for instance.

Natural Gas Flow

To understand combustion appliance in-use efficiency, it is important to properly measure natural gas flow rate into the appliance. Gas volumes vary with pressure and temperature, it is common to have a gas meter with temperature compensation features.

Many times, long term monitoring is required to determine installed efficiency for furnaces and boilers or gas water heaters, so robust and reliable gas meters are required. To properly calculate the amount of heat delivered to the combustion appliance, local heating value must be adjusted properly.