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. Due to the wide range of flow rates that these measurements may include, there are different types of flow meters. Due to cost requirements, volumetric flow meters are typical even though there are flow meters that can measure mass flow rate directly.
A turbine flow meter, installed under a sink, is used to measure the hot water flow rate and total usage. Credit: Dane Christensen, NREL
The most common type of flow meter for residential field test applications is a turbine flow meter. Turbine flow meters come in a variety of size and resolution options and are typically used in conjunction with hot and cold water flows. Measuring condensate flow rate, however, is not a measurement that turbine flow meters do well. Condensate is generated at a very slow flow rate and is not necessarily a continuous flow. There are ways to very accurately measure condensate flow rate in a laboratory setting, but they are cost-prohibitive for a field test. A pumped reservoir is a type of flow meter that is appropriate for field tests when measuring very low liquid flow rates. A tipping bucket rain gauge is another device that can be used to measure condensate generation rate.
There are a number of other ways to measure liquid flow rate, some of which are not expected to be used often in field tests. The following list of flow meters includes those that are commonly used in field tests and some that are not.
Costs apply to equipment designed for flow rates of up to about 15 gpm, except in the case of the pumped reservoir, which is most likely to be used for condensate measurement at much lower overall flow rates.