To get an idea of how much HCFC-22 is being used in the industry, just realize that the refrigerant has applications ranging from residential air conditioners to large flooded chillers. In that later category, British Energy PLC - said to be the largest electricity generator in the UK by volume - was seeking to replace R-22 in its chillers.

The headquarters site at Barnwood, Gloucester, operates the data centers for the eight nuclear power stations in the UK. As part of their environmental strategy, British Energy has already converted all of the site’s systems from R-22 to non ozone depleting replacements, but has until recently been unable to find a suitable alternative to R-22 for the flooded chillers. This was of considerable concern in view of the imminent phaseout of the use of virgin R-22 for service work (in Europe), and the fact that replacement of a chiller of this size would cost over $815,000.

British Energy engineers had experimented with at least one R-22 retrofit alternative but after trying that HFC found that the chiller could not achieve the temperature difference across the evaporator. So in May 2009, they pulled that refrigerant and tried another HFC, R-434A.

The chiller has a screw compressor that is 30 years old with a flooded evaporator. There is a pilot operated thermostatic expansion valve and partial hand expansion valve. There is a heat recovery circuit on the condenser

The original charge was 2,640 pounds of R-22. It was charged with the same amount of R-434A. The mineral oil and the retrofitted POE oil both have a viscosity of 170.

IN CONTROL

The control system operates a compressor unloader system based on a number of inputs which include - but are not limited to - chilled water leaving temperature, suction pressure, discharge pressure, and motor loading percentage. The following readings were taken five months after the retrofit:

SUCTION PRESSURE: 74.32 psig
DISCHARGE PRESSURE: 188.30 psig
MOTOR AMPS: 50 (Maximum setting 80, FLA 120)
ENTERING CHILLED WATER TEMPERATURE: 51.08°F
LEAVING CHILLED WATER TEMPERATURE: 46.010 (set point 46.40)
SUCTION TEMPERATURE: 41.9°
EVAPORATOR SUPERHEAT: 35.780
MOTOR LOAD: 55.62 percent
OUTSIDE AIR TEMPERATURE: 62.6°

According to statistics compiled by ComStar International (which markets R-434A under the brand name RS-45), energy usage would appear to be lower with R-434A with 410 achieved at 65 amps, against design of 41.90 at 108 amp. The system was operating up to 41.90 temperature difference on chilled water, which was equal to design capacity.

“Before the initial conversion from R-22 to the previous HFC, the lubricant in the chiller had been changed from mineral oil to polyolester,” it was reported. “The superheat was very consistent and did respond to adjustments to the expansion devices. Overall the customer is very happy with the performance of the chiller as it appears to be very similar to the R-22 performance.”

John Bravery of engineering contractor Balfour Beatty oversaw the conversion of the chiller with John Ormerod of refrigerant supplier A-Gas UK in attendance. Bravery said the changeover process was quite straightforward. He said there were no problems with this chiller since the changeover.

Geoff Benton, British Energy’s site engineer, said, “We have been planning to phase out R-22 on this site before the cut-off date for using new R-22 for service work kicked in at the end of 2009, but finding a refrigerant which can match the performance of R-22 in the flooded chillers here had not been possible until the arrival of R-434A. The fact that using this refrigerant to replace R-22 in one of our flooded chillers has resulted in an identical performance to using R-22 in this unit means that we will be converting the remaining flooded chiller on site, and thereby achieving our overall objective to be free of ozone depleting substances prior to the phaseout date in Europe. Overall, we are very pleased with the performance in what I understand is one of the most difficult applications for R-22 replacements.”

For more information on the refrigerant described in this article, visit www.comstarproducts.com.

Publication date: 01/11/2010