Today's Heat Pump Reliability Issues
Today the industry is facing new challenges. The move to higher-efficiency unitary systems has resulted in increased use of thermostatic expansion valves (TXVs) instead of cap tubes, and these metering devices have their own idiosyncrasies (see "So Many TXVs to Troubleshoot" in this issue).
In fact, a study on "Field Measurements of Air Conditioners (and Heat Pumps) With and Without TXVs" (Robert J. Mowris, Anne Blankenship, and Ean Jones, Robert Mowris & Associates) states that, out of 6 million new residential and light commercial split systems, heat pumps, and small packaged air conditioners installed annually, "approximately 50-67 percent ... are installed with improper refrigerant charge and airflow, causing them to operate 10 to 20 percent less efficiently than if they were properly installed."
So where are the energy savings customers were promised? What will this do to their perceptions of the product?
Actual heat pump reliability has increased dramatically, according to a report given at the 2005 International Energy Agency Heat Pump Conference. But can positive customer perceptions be maintained in spite of changes in the products and the market? According to some equipment manufacturers, the quality of the installation will again play a critical role.
TODAY'S PICTURERaymond Granderson, supervisor of training products and services for Rheem Air Conditioning, said he sees a couple of different things going on in today's heat pump market.
"I see consumer awareness of heat pump reliability and contractor confidence in heat pumps. In order to keep building consumer confidence, techs need to be proficient in the product.
"Electric utility promotions are increasing consumer awareness," he said. "They are looking to contractors to provide those products."
He chuckled and said, "When I worked in the field, we had jobs that were less than perfect. We learned some expensive lessons."
Tim Lashar, outdoor products manager and LuxaireÂ® brand manager for York, a Johnson Controls Company, cited current issues that could affect customer perceptions:
He also cited quiet operation, aesthetics, and comfort as consumer issues that may become contractor issues.
INSTALLATIONS AND REPLACEMENTSWhen it comes to replacement installations, the operation of new heat pump equipment can be heavily affected by the quality and type of system it is replacing.
"Older installations that were sized primarily for heating may not have adequate ductwork for cooling requirements," Lashar said.
Granderson said that during installations, particular care needs to be given to the air side. "Heat pumps are not as forgiving as conventional air conditioners," he said. "The contractor really needs to pay attention to the details. The single largest issue is inadequate airflow on the indoor side."
The cause, he said, could just be a poor or undersized duct system. "The indoor unit cannot move the air it needs to. During heating operation, it's really critical. If the airflow is not correct, it skews the refrigeration system's operation, which winds up having an adverse impact on the refrigeration side. Techs may misinterpret this as a refrigerant problem and add or remove refrigerant, and it's really an airflow problem."
Duct leakage can lead to problems, agreed Lashar. "Older installations that were put in before new, stricter building codes may leak up to 20 percent or more of the total air volume, reducing efficiency and airflow to the space," he said. "In many cases, the ductwork is inaccessible and cannot be changed. These issues, however, need to be addressed by the dealer as best as possible."
Systems that use R-410A have special issues. "Refrigerant and oil incompatibility and coil surface area are just a couple of issues that must be addressed," Lashar said.
Contractors need "complete understanding of the heat pump system, not only the cooling side but the heating side, airflow, and refrigerant - a good global understanding of heat pumps," Granderson said. "They simply may not understand that the ductwork is undersized, or the refrigerant line is too small, or coils are mismatched. You can get into trouble very quickly - it really throws the refrigerant side askew very quickly."
These problems aren't new, he added. But they are more critical when it comes to heat pumps, than with cooling-only central systems. And newer systems may be more strongly impacted. "An air conditioning system is a little more forgiving," Granderson said. "But the heat pump, because we're operating in cooling and heating, the tolerances, the forgiveness factor is not nearly as great."
COIL SIZEIn general, contractors have been doing a good job of making sure that indoor and outdoor coils are properly matched. However, if the higher-efficiency system has a much larger indoor coil than the unit it is replacing, should contractors be more tempted to leave the old coil in place?
"The new sizes can be a very big issue," Granderson said. "In a retrofit, for instance, they may not have room to put in a new indoor coil; we're dependent on the indoor coil for the heating mode. Performance and efficiency will suffer at the very least" if that indoor coil is not properly matched to the new system.
"In the long run, it will be better for the homeowner to have the entire heat pump system replaced," said Lashar. "They will gain the benefits of motors that are more efficient, and compressors and evaporator coils that have been designed to provide optimal efficiency for its matching heat pump."
In addition, "Both service and installation can and will be substandard unless all technicians are properly trained," Lashar said. "Risks may seem larger when it comes to an improperly installed system, but try to explain that to a homeowner who has had to meet a service technician at home on numerous occasions because of a poorly serviced or installed unit."
EQUIPMENT CHANGESMany newer heat pumps have features that help improve their operation and serviceability. Right now they are found on top-of-the-line products like these.
"Our product incorporates a control board for the outdoor unit that monitors the compressor," Granderson said.
"It's a diagnostic aid for the technician called the Comfort Control system from White-Rodgers. It offers active protection and monitors the system; a pressure switch communicates to the control, so the technician has a starting point for troubleshooting." A flashing light alerts homeowners to potential problems.
"The ECM motor also helps heat pumps go beyond those airflow issues," Granderson said. Using a programmed configuration and dipswitches, the technician can set up the unit to deliver a certain amount of airflow.
"The motor can ramp up or down to deliver the correct amount of airflow. It can overcome poor duct systems to a point." The ideal solution, of course, is to fix the ductwork.
Lennox said it has "continually tried to improve upon heat pump reliability and the tools provided to service technicians." The Lennox System Operations Monitor (LSOM) can monitor and collect data to provide visual indicators of potential system faults. The company says this "greatly improves troubleshooting accuracy and technician productivity."
Demand defrost boards with self-monitoring diagnostics can sense the temperature on the condenser coil and activate the defrost mode as needed, the company said. Specific to R-410A systems, the company uses specially designed scroll compressors and reversing valves with a more robust slide mechanism.
York's 18 SEER Affinityâ„¢ unit uses the Ultratechâ„¢ compressor as part of the QuietDriveâ„¢ system.
"QuietDrive utilizes a swept wing fan design, isolated compressor compartment, composite base pan, and two-stage cooling to provide four times' quieter operation and 60 percent more energy-efficient performance," Lashar said.
The Affinity 8T heat pump features hot heat pump technology "that produces discharge temperatures that are, on average, 10°F warmer than the discharge temperatures of standard heat pumps," he said. The unit can reach up to 18 SEER when matched to a York variable-speed furnace or air handler. It is available with HSPF ratings of 8.0 through 8.5, and is Energy StarÂ® qualified.
The Affinity heat pump offers a full-end, full-service access panel with a handle, Lashar said an isolated compressor compartment, easy-access side-discharge service valves, and an adjustable knockout plate for electrical whips. The unit also features a solid-core filter-drier, demand-defrost board with service analyzer capabilities, integrated control, fault code retention, hot heat pump and fossil fuel jumpers, high- and low-pressure switch connections, and special features to protect a home against pipe freeze-ups.
STILL RELIABLE"Heat pumps simply operate with greater reliability than they used to," said Lashar. "Some homeowners still have bad tastes in their mouths because of the way some heat pump systems operated 25 years ago. But, with homes being built with better insulation and heat pumps achieving higher outlet air temperatures, that stigma is going away.
"Dealers must educate homeowners and be sure to offer the choice that will provide the highest level of economical comfort," he said. "With the recent jump in gas prices, even without local utility rebates, heat pumps are once again a viable option in most parts of the country."
"In those situations where the equipment isn't properly matched and indoor airflow is inadequate, [consumer perception] will be at risk," Granderson said. "If those are done properly, it will be on the flip side; it will increase reliability."
Publication date: 05/22/2006