When there is excess
oil in an operating chiller, it can cost a small fortune in higher
operating costs and decreased capacity. Below is a classic
example.
Bob Lee is a chief engineer for Harbor Group Management Co., a
property management company. He is responsible for the maintenance
of a 27-story office tower in Cincinnati.
“I had originally been an engineer in this building from 1990
to 1994, and the systems ran fine during those years,” said Lee.
“Then I was brought back by Harbor Group in 2002 after they had
acquired the property. I noticed efficiency problems with all
three chillers right away.”
Bill Adkins, Chiller Group manager for DeBra-Kuempel Mechanical
Contractors in Cincinnati, had been servicing the Carrier 19EA
575-ton chillers since they were installed 20 years ago. He helped
explain the chillers’ performance degradation.
“The problem with excess oil started when the previous owners
sold the adjoining building,” said Adkins. “It had been built
after the office tower and was interconnected to the original. To
economize, they used the newer building’s flat-plate chiller to
cool the original building during the low-load times of spring and
fall. That meant the three chillers only ran at higher loads
during the summer. After the sale, the chillers ran for extensive
stretches at low loads and the oil began to migrate to the
refrigerant side.”
“When I came back to the building as chief engineer, I
immediately noticed the lack of efficiency,” said Lee. “These
chillers had a design efficiency of 0.89 kW/ton — very good for 20
years ago when they were installed. Now they were running between
1.1 and 1.5 kW/ton, and I wanted to know why. I called Bill Adkins
and asked him to find the problem.”
There weren’t too many things to look at. Every year the
DeBra-Kuempel technicians performed oil and refrigerant analyses.
They did extensive preventive maintenance, and every six years
they tore down each chiller for a complete overhaul.
“I was surprised when we discovered the excess oil,” said
Adkins. “With the annual refrigerant analysis, we thought we had
it under control. But those long, low-load conditions took their
toll. We found 15- to 20-percent oil in the three chillers.”
The technicians were able to pump the refrigerant load into the
evaporator, boil the refrigerant back into the utility vessel, and
remove the oil that remained in the vessel. It is a lengthy and
costly procedure. Moreover, every time oil levels rose to a point
that significantly degraded efficiency, the procedure would have
to be repeated.
“If we could run steadily at 90- to 100-percent efficiency, we
wouldn’t have an oil problem,” said Adkins. “But you can’t get
away from spring and fall and mornings and evenings. So we were
always on the lookout for some more cost-efficient
solution.”
