Airflow, Charge, And Comfort

April 4, 2005
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In addition to looking at customers' control configurations to figure out why they have hot or cold spots, it is critical to check that the system has proper airflow, both on the supply and return air sides, and that the system has a proper refrigerant charge. In fact, you will want to make sure that these criteria are examined before you start selling new thermostats or zoning products.

If you sell a new control system but there is poor airflow to one or more rooms, the customers still won't be comfortable. You will not solve their problems, and you will not gain their trust. New equipment will only be a Band-Aid on a much deeper, more insidious problem.

Airflow Diagnosis

A poorly performing duct system can affect customer comfort, system output, energy consumption, system longevity - the gamut. But how many contractors regularly measure the performance of the duct system when they are troubleshooting a unitary system, or even installing a new system? The answer is, not enough.

Part of the problem is ego. If you find out that your own work isn't as good as you thought it was, that can be hard to take. Finding another company's errors is a little less bruising.

A properly balanced system makes all the high-tech engineering and design worthwhile. Without proper balancing, the customer just doesn't get what he or she paid for.

To really, truly diagnose a system problem, a tech needs to measure airflow, static pressure, temperature delta across the heat exchanger, refrigerant superheat and/or subcooling, humidity, rpm, amperage, voltage, and delivered Btu. Measuring airflow also can take the contractor out of the realm of selling a commodity.

Airflow diagnostic tools and instruments include an air balancing hood, digital manometer, hot wire anemometer, rotating vane anemometer, static pressure tip and pitot tube, thermometers, smoke devices, amp/ohm/volt meter, and a variety of hand tools (good drill with 3/8-inch bit, 3/8-inch test hole plugs, additional hood sizes, good flashlight, calculator, 6-foot folding ruler, clipboard).

Airflow hoods have varying capacities, limitations, and reading characteristics. If a grille is in a place where a hood cannot be used (such as in tight spaces), use an air traverse instead. Cover the grille's open area completely with the balancing hood. Make sure you have a tight air seal. Then read and record the cfm reading on the meter.

The Refrigerant Charge

An insufficient refrigerant charge, or too much refrigerant in the system, can lead to comfort problems, or worse, a shortened life for the compressor, especially in heat pumps. For instance, if the line set is installed with a longer run than the manufacturer has charged the unit with refrigerant for, not enough heat will be supplied when the customer needs it.

Too much refrigerant can remain in the system if the amount of line used is less than the manufacturer has charged the system for (typically 25 feet), resulting in excessive heat pressures.

Higher-efficiency equipment tends to be intolerant of poor charging practices. Some newer refrigerants also require more care during charging. Measuring a system's superheat and subcooling is essential for determining the system's correct charge.

Inexperienced and/or untrained installers, for instance, may not pull a good vacuum on the system. They may not even keep charging scales in their vehicle. Without these tools it is next to impossible to ensure that the proper charge is applied.

It may not be possible for all contractors to train all installers as well as they train their technicians. However, all contractors would benefit from having a double-check system in place to check the critical parameters - airflow, pressure, temperature, humidity, rpm, amperage, voltage, delivered Btu, refrigerant charge (including superheat and subcooling) - of newly installed equipment.

Give your installers a checklist. Have them call a service supervisor to review their readings. It will save you callbacks and increase customer goodwill.

Remember, you can't control what you don't measure.

For more information, click on the Emerson Climate Technologies logo above.

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