Engineering Refrigeration Systems — A Forgotten Skill
When a building owner asks application and design questions, a consultant must be able to ‘talk the talk.’
With variable refrigerant flow (VRF) HVAC systems growing in popularity, engineering refrigeration systems can become very intimidating to many design engineers. I know from my own professional experience, as I have had to brush off the cobwebs from my ASHRAE Handbook-Refrigeration and refresh myself on designing refrigeration systems.
Back in the 1980s, I joined a mechanical contracting firm that had been around since the 1940s and had in-house refrigeration design engineers who were more comfortable with the engineering design of these systems versus chilled water systems. A few of these engineers were also very comfortable and knowledgeable with ammonia systems. It was a technical environment unlike any of the consulting engineering firms involved with design-bid-build and construction management project delivery. For the most part, this firm was focused on design-build (D-B), and while we were very successful with this type of HVAC project delivery on projects like chiller plant expansions, we were also very successful with engineering built-up mechanical cooling systems for the industry through projects like plastic mold equipment manufacturing using refrigerant rather than chilled water. There were some really cost-effective benefits to using refrigerant in lieu of chilled water until the Montreal Protocol started to influence mechanical cooling applications.
I worked at this design-build, HVAC service company for nine years and learned so much more about practical refrigeration application because the professionals and service technicians there could put together these types of systems just like an erector set (or Legos, for those younger designers who don’t know what an erector set is). Each engineer would size the solenoid valves, expansion valves, refrigerant driers, compressors, and refrigerant lines — to mention some of the pieces that made up these refrigeration systems.
It was fascinating so see all the components that went into a direct expansion cooling or dehumidification installation. Who does this when it comes to more conventional chilled water design? The answer is the equipment manufacturer does the majority of design engineering of the refrigeration equipment, like a 400-ton, variable-speed drive centrifugal chiller. The consulting design engineer determines the size of the refrigeration chiller, but that’s about it. After that, this design engineer will determine the chilled water pipe size and condenser water size as well as provide the electric data to the electrical engineer to accommodate the chiller electrical power, but even here the equipment manufacturer provides the right chiller motor starter for the application.
Years ago, I was responsible for a very innovative chilled water system that included a 600-ton chiller in series with two 300-ton chillers and three water tanks of 275,000 gallons each for thermal storage. When someone asked me how difficult it was to come up with this specific application, I said, quite seriously, “Heck, the refrigeration engineering was all done by the equipment manufacturer. All I had to do was show where the chilled water and condenser water pipe connections were on this equipment.” I went on to say, “If the chiller came with a plug and there was a larger enough electric wall outlet, I could have simply plugged the chiller in.”
My point to that conversation and to the subject of this month’s column is that consulting engineers don’t often get the opportunity to engineer the refrigerant side of an HVAC application. Equipment manufacturers complete, for the most part, the refrigeration engineering, and the old-time refrigeration design engineers have long since retired from the consulting engineering community responsible for HVAC building system design.
VRF applications have been around since the 1980s, but their incorporation into consulting engineers’ areas of expertise, e.g., office buildings, schools, hospitals, etc., has taken several years. With these refrigeration applications becoming more common, consultants need to brush up on their refrigerant fundamentals. Sure, some consultants will draw upon VRF sales engineers, but when the building owner asks application and design questions, the consultant needs to “talk the talk” and be able to explain the difference between the few VRF equipment manufacturers’ engineered design of their equipment.
Just like myself, other consultants need to brush off the cobwebs on their ASHRAE Handbook-Refrigeration and become more familiar with the issues and concerns associated with refrigerants. Consultants are already familiar with the issues and concerns with the application of gas, fuel oil, and electric heat. Refrigeration is back!
Next month, I’ll examine design engineering of steam systems — yet another often forgotten application.