Expansion Valve Helps Improve Efficiency

October 13, 2008
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A TXV retrofitted to an existing older system can greatly increase SEER. Note that the sensing bulb and tubing are wrapped with insulation. (Photo courtesy of Danfoss.)

No longer just a dire prediction, budget-breaking energy costs have arrived in the United States, long fortunate to have among the world’s very lowest utility costs. Though the winter of 2007-08 was relatively mild in many areas, consumers were still beset by utility bills that increased by 50 percent and more over prior years. Further increases are happening - and have occurred - during this year’s summer cooling season.

Pressed by federal regulations to improve energy efficiency by a measurable 30 percent, air conditioning system manufacturers redesigned hundreds of units in their product offerings to meet the new 13 SEER requirement, which became effective in January 2006.

In 2001, five years before the requirement was to go into effect, Danfoss began development of an expansion valve, type TR6, designed specifically to improve the efficiency of new residential air conditioning systems. Testing of the new valve on systems in both Danfoss and OEM laboratories showed that the improvement in efficiency over the fixed orifice devices previously in use was significant and would be a major contribution to meeting 13 SEER.

With further work by the manufacturer and OEM engineers, compliant new systems could be offered by the 2006 deadline at more reasonable prices than had been expected.



ADVANTAGES

The advantage of a thermostatic expansion valve (TXV) - like the TR6 - over previously used fixed orifice regulation is that a fixed orifice device constantly delivers the same amount of refrigerant to the evaporator regardless of the living space load on the system. With a fixed orifice, when temperature is lowered to the desired level, then rises a bit, the system comes on and delivers the same maximum cooling that was required for a large temperature drop. The compressor runs full out, using maximum energy, for its fixed minimum run time.

In contrast, an expansion valve has a sensing bulb that constantly monitors the evaporator and varies the flow of refrigerant so that the evaporator is used with maximum efficiency. This means that when the requirement for cooling is reduced, which is the case about 70 percent of the operating time, flow is reduced by the action of the TXV, there is less flow, the compressor does not work as hard, comfort is improved, and considerable energy is saved.

“Designed with its patented features specifically for residential air conditioning, the TR6 valve is a very efficient solution,” said Robert Hennessy, director of aftermarket sales at Danfoss. “It provides air conditioning manufacturers significant help gaining the efficiency improvement needed to meet the federal regulations for new equipment. And the new efficiency will be greatly appreciated by homeowners as utility rates increase.”



THE PROBLEM AND SOLUTION

There are many more homeowners, not limited to those in the United States, with existing air conditioning systems manufactured before 2006 that are still working very well. With regular seasonal checkups and maintenance, most of these older systems can give service and comfort for many more years. The cost of continuing operation, though, could be painful. Unfortunately, the cost of a new, highly-efficient system is for most homeowners prohibitive, and payback would be many seasons coming.

“At Danfoss, we approached this problem in our spirit of EnVisioneeringSM,” said Hennessy. “The solution seemed to lie in fitting an expansion valve to an existing residential unit and reaping the savings. Laboratory tests demonstrated that installation could be accomplished by a technician in the field, and verified the increase in unit efficiency. All tests said, ‘Go.’”

There was one problem: the variety of air conditioning systems - some 20 years old or more, many newer - used three different and incompatible styles of connection. That could mean that service technicians would have to carry three valve models in each capacity as truck stock.

The solution? In early 2006, a valve kit was developed that included all three types of connections found on existing residential air conditioning systems. The kit contained a TR6 valve along with sweat, Chatleff, and Aeroquip fittings. The kit was dubbed the Universal TR6.

Initially, there were many questions about the new kit. Contractors wanted to know how much could be saved and, most importantly, how long it would take a technician to install and adjust the valve.

To answer these questions, application engineers at Danfoss undertook a field test to provide the needed data about actual savings from a Universal TR6 upgrade, to determine how much time a field technician would need to install the upgrade, and also to study best practices for the installation.

For the test, homes of average size (2,300 square feet) were chosen, with air conditioning and heat pump systems in service over a wide range of time and in a range of sizes. To isolate savings to the valve installation, each system was checked for other factors that might influence results: indoor airflow and filter cleanliness; indoor and outdoor coil cleanliness; proper refrigerant charge; proper sizing of the system for the residence; and that customers were, overall, satisfied with system operation and comfort provided.

Universal TR6 valves were installed, with best practices for an efficient installation being noted by the application engineers for all three types of connections - solder, Aeroquip, and Chatleff. Then, using the power monitoring capabilities of a Danfoss AK-SC 255 rack controller, power consumption for each system was recorded before and after valve installation. Indoor temperature and humidity, as well as mechanical system temperatures and pressures, were also recorded. Data were adjusted for degree days.



AVERAGE SAVINGS: 27.8 PERCENT

The results of the field test showed an average savings in kilowatt-hours of 27.8 percent. Using the best practices followed by the application engineers for the installations, about 4.5 labor hours were required, and at prevailing average labor rates and utility rates, it was roughly estimated that the homeowner’s utility savings would pay for the upgrade in nine months of operation (which, in the Chesapeake region, would be less than two air conditioning seasons).

In addition, indoor comfort was better, with lower humidity, using a TXV rather than a fixed orifice device.

For more information, visit www.danfoss.com/North_America.



Mount the sensing bulb on a straight section of pipe as close to the manifold as possible. The copper strap should be tightened until the refrigerant tubing is just slightly deformed. (Photo courtesy of Danfoss.)

Sidebar: Bulb Installation

For the TXV to properly deliver a changing flow of refrigerant that matches the load on the cooling system, the bulb must be placed just after the suction header. It must be installed where the tubing is straight, not on a bend of any degree.

The contractor should ensure that the bulb is in good contact with the tubing, and secure it very tightly with a copper strap, slightly deforming the refrigerant tubing, to enhance heat transfer. Then the contractor should wrap insulation around the bulb and tubing where they are attached.

For reference, see photo at right.

Publication date: 10/13/2008

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