Valves applicable for these test procedures include all types of automatically controlled hydronic valves that serve heating and cooling coils on air handlers, fan coil and terminal units, and radiators, as well as automatic isolation valves on chillers, cooling towers and boilers.
Valve Configurations and Preferred Test Methods
Air Handler Unit Heating and Cooling Coil Valves - For air handlers with valve flow rates of 30 gpm or more, a test that will detect small leaks (<15%) is warranted on most valves. For this application, the Balancing Valve Method is preferred. When valve flow rates are between 15 to 30 gpm, testing a smaller sample, like 30%, is more appropriate. However, the Balancing Valve Method is still preferred to detect small leaks. For valves with flow rates less than 15 gpm, refer to the Air Terminal and Fan Coil section below.
Air Terminals, Fan Coil Units and Fin-Tube Radiators - Typically these devices have small copper piping with small valves and no test ports or other means of measuring the temperature of the water directly. The air stream may or may not be monitored by the BAS. The energy penalty for an individual device is small for minor valve leakage because the design flow is so small. However, in most projects there is a large number of terminal devices, which typically justifies testing for leak-by using a sampling strategy. When the air terminal unit discharge air temperature is not monitored, the preference is to look only for larger leaks using the Infrared Thermometer Method on a large fraction of the total units. An alternative approach for air terminal units is to rigorously check a sample of 10% to 15% of units using the Coil Drain Down Method to detect both small and large leaks. When discharge air temperature for the air terminal unit is available, using the Air Temperature Across Coil-30 minute Test method or the Infrared Thermometer Method is preferred.
Automatic Isolation Valves - The Balancing Valve Test (often a triple-duty valve) on parallel chillers and boilers is the preferred method, because it is efficient and provides confident results, unless an insertion flow meter has been installed.
It may not be necessary, or economical, to test every single valve for a given project. The number of devices tested and their acceptance criteria depends on the how critical valve leak-by is to either system operation, energy consumption, or thermal comfort. Sampling is a method that seeks to balance reliable results with a reasonable amount of effort. Suggestions for sampling rates are given in the previous sections, but typically project specifications will stipulate either a given sample percent or a minimum number of systems that must be tested. Then if a given percentage of the samples fail, all remaining devices must be tested or sampled. Note that in order to make sampling effective, selection of the devices for testing should be done randomly.
Corrections to Leaking Valves
If a valve is leaking by, check that the valve stroke time programmed into the BAS is 10% or 15% longer than the specified stroke time of the valve actuator. For pneumatic actuators try increasing the pressure. The valve close-off pressure should be at least equal to the pump’s operating pressure. ASHRAE recommends 150% of the pump pressure. Check that the valve closes under the force of the actuator, not the spring if the valve actuator is equipped with a spring. Check the close-off specifications for the valve and compare to the water pressure in the piping to make sure the valve has the capacity to completely close off against the water pressure. Other possible causes for inadequate closure are incorrect wiring, sticking components and damaged valve components caused by cavitation from oversized valves.
Each test method requires a different set of tools, as explained in the respective test procedure. In general, typical test equipment can include:
- Differential pressure gauge
- Digital thermometer
- Infrared thermometer
- Ultrasonic flow meter
All test equipment must provide accurate readings in order to verify system performance. For all the methods described in this document excluding the Infrared Thermometer Method, the absolute accuracy of the measuring instrument is not critical if the intent of the test is to measure a differential value and the same instrument is used to make both measurements. The reason is that measurement error will be subtracted out when calculating a differential value. Instruments with accuracies of ±1.0°F for temperature and ±3% of full scale for pressure transducers are sufficiently accurate for this purpose. However, since pressure transducer accuracy is typically rated against full scale, it is recommended that the pressure transducer selected for use is close to the expected pressure. For example, a 0-300 psi transducer should not be used if the expected pressure range is between 30 to 40 psi.
Direct flow measurements using the installed flow meter(s) or a portable ultrasonic flow meter are more susceptible to inaccuracy in the measuring device. Installed flow meters are normally sufficiently accurate if they have been factory calibrated, installed correctly, and then used on clean water. Ultrasonic flow meters have good accuracy potential, but are very sensitive to pipe conditions, user set up and user application.
The location where the readings are taken is very important. Often the most difficult issue with any temperature-based leak-by test method is identifying an acceptable location for the hand-held temperature measuring instrument. Each project will have a different set of choices for taking temperature measurements of the water in the piping. Below is a description of these choices listed in order of the most preferred (easiest and most accurate) to least preferred. See Figure 1 for an illustration of a typical air handler coil with marked temperature measurement locations. Note that the gauges in this particular application can’t be used for temperature measurements because they are not fitted with isolation petcocks.
Figure 1. Typical Air Handling Unit Piping
P/T Ports - P/T (pressure / temperature) ports are designed for a hand-held metal temperature probe to be inserted directly into the water stream. In many cases even a thermocouple wire end can be carefully pushed through the hole in the rubber seal of the port and into the water. These ports also are used directly for taking pressure measurements.
Thermometer Wells - To use a thermometer well to measure temperature, unscrew the thermometer and insert the end of the handheld instrument’s thermocouple wire to the end of the well. Using heat transfer grease around the thermocouple is ideal, but not necessary. Close off the opening of the well to prevent heat exchange with the ambient air with insulation (if insulation is not available, use crumpled paper or cloth.) Response time to temperature changes in the water are slower than with sensors directly in the water by 1 to 3 minutes.
Pressure and Temperature Gage and Vent Fittings - Pressure and temperature gauges installed with isolation valves between the gauge and the main pipe can be used to measure water temperature directly. Close the isolation valve and remove the gauge. Insert the handheld instrument thermocouple into the open pipe end and slowly bleed water out past the thermocouple, letting the water drop into a bucket. A fitting setup with a P/T port for the thermocouple and bypass drain hose offers a “cleaner” test.
Pipe Surface - If there are no appropriately located ports, wells or gauges take temperature measurements directly on the outside of the pipe. For the Water Temperature Across Coil Method find a location at least 3 or 4 feet away from the coil so that the pipe wall temperature at the hand-held sensor is not affected during the test by the change in coil temperature. If the pipe is insulated, make a small slice through the insulation, slide the thermocouple wire under the insulation, and get it directly against the pipe surface. Slide it back and forth a few times while observing the temperature reading until good contact is made (i.e. measured temperature is close expected temperature). Tape the wire to the outside of the insulation, if necessary, to keep thermocouple from moving around during the test. Once the test is completed, make sure to tape over the slice with appropriate vapor-barrier tape to prevent condensation potential. For bare pipe, wipe any dirt and dust off the pipe and place the thermocouple directly on the pipe. Secure it in place with duct tape and cover with 1/2” foam or 1” or more of fiberglass insulation, extending at least four inches on all sides of the thermocouple.
1.1 Create a test form - Testing will be easier, more conclusive and efficient if the test procedure is thought through and documented before conducting the test. Developing a test form will assist in data collection and subsequent evaluation and may allow less experienced staff to execute the tests.
1.2 Determine acceptance criteria - Leak-by tests are normally a simple pass/fail based on whether there is leakage. Determining minor leakage on every valve may not be practical or cost effective. Hence, the tests should focus on those applications that can contribute to energy waste or lead to control problems. In these applications, any leak-by result designates a failed test.
1.3 Provide instructions/precautions - Operating the system with no-flow through a coil during the test for more than 30 minutes may lead to indoor comfort complaints if the space is occupied. Negative building pressures and potential condensation in hot and humid climates can also be a problem, if the associated exhaust fans are not shut down when supply fans are turned off.
1.4 Specify participants and roles/responsibilities - The testing guidance provided in this document can assist in verifying proper system performance in both new construction and existing building applications. The following people may need to participate in the testing process. Refer to the Functional Testing Basics section of the Functional Test Guide for a description of the general roles and responsibilities of the participants. These roles and responsibilities should be customized based on actual project requirements.