SEER Ratings and TXVs

QUESTION:
From Randal Ripley
Nashua, N. H.

What increase in SEER rating is achieved going from a flow-rater fixed metering device to an expansion valve provided all else stays the same?

ANSWER:
By Emerson Climate Technologies

To explain why a system’s Seasonal Energy Efficiency Ratio (SEER) rating is improved by using a thermal expansion valve (TXV) instead of a fixed orifice device, we need to first understand how the SEER is determined. The SEER is a measure of how efficiently an air conditioner or heat pump will operate over an entire cooling season instead of only a single operating condition.

For single-speed systems, the SEER is calculated as follows:

SEER = EERb*(1 – Cd/2)

Where:

EERb = energy efficiency ratio at 95°/75°F (dry bulb/wet bulb) outdoor temp and 80°/67°F indoor temp

Cd = cyclic degradation coefficient determined through two dry coil tests (one steady state, the other cyclic). This factor quantifies the part-load (cycling) efficiency of the system.

In order to improve SEER, it is important to keep the Cd as low as possible. This can be achieved by minimizing the amount of refrigerant entering the evaporator during the “off” cycle. With a fixed orifice device, the high and low sides of the system equalize during the off cycle, resulting in a high Cd. In comparison, a nonbleed TXV closes tightly when the compressor shuts off, preventing equalization and thereby minimizing the Cd. It is for this reason that TXVs will typically increase the rating of an HVAC system by approximately 0.5 SEER.

It should be noted that a system can be designed with a fixed orifice and liquid line solenoid to achieve a SEER rating equal to that with a TXV. However, such a system would not be as efficient over the entire operating range of the equipment as it would with a TXV. The TXV regulates the flow of refrigerant to maximize the efficiency of the evaporator at all operating conditions, whereas a fixed orifice can only be optimized at one particular condition. For this reason, if energy efficiency is the goal, a system incorporating a TXV should be specified.

Selling Equipment to Do-It-Yourselfers

COMMENT:
By Robert Dickinson
The Air Conditioning Store
Charlotte, N.C.

A previous question to the Hotline asked if a contractor selling split system air conditioning equipment to the do-it-yourselfers (DIY) is in violation of Environmental Protection Agency (EPA) refrigerant laws. We have sold systems, including ductwork, etc., to that market for close to 15 years, as a part of our contracting business. Our structured selling system prevents such possible EPA violations. The first line in our price sheet to the DIY states the necessity of “permanently connecting refrigerant lines to both the condensing unit or heat pump outdoor unit, and to the evaporator coil; balance refrigerant charge, and check, test, and start the system for satisfactory operation.”

There is a charge for this and a stipulation that the refrigerant lines and control wires are in place, are not broken or kinked, and are extended to a point that will not require additional refrigerant line material or fittings. The incentive is for the homeowner to let us do the work, since there is no financial advantage to do otherwise. We have sold hundreds of these systems to this type of market and have never been questioned as to who does this work.

Teamwork: Four Heads Are Better than One

COMMENT:
By John West
Chesterfield, Va.

You might call the following, “teamwork in action.” We received a complaint about a compressor that was not pumping. We ordered another compressor and had the same symptoms. We called a factory rep to come out, but before that person had to come, we solved the problem. The unit in question was a McQuay liquid chiller outside unit and Copeland scroll compressors.

The situation was that the unit called for compressor 1 and then 3 and then 2 and then 4. One and 3 are tandem and 2 and 4 are tandem. When we ran compressor 3 by itself, we had these readings each time: discharge line, 126°F; suction line, 120°; suction, 97 psig; discharge, 125 psig; amps, 14.6, which was one-half of the 25.5 rated load amp (RLA).

By running 1 and 3 together, both compressors had normal readings. It was brought up among us that it looked like a check valve was not working somewhere in the system. Returning to the shop, we brainstormed as a team and researched with the Copeland reference material. It looked like we were on the right track.

Returning to the jobsite the next day, compressor 1 was pulled and, sure enough, there was a defective check valve. We put in a new compressor and all worked well. My team members on that project were David Jewell, Keith Rowland and Tom Sizemore.

This incident is an example of what teamwork is all about.

Publication date: 09/22/2008