About the authorMike Fisher has over 35 years of experience with refrigeration systems. This background includes; service, installation, equipment manufacturing, research and development, project management, consulting engineering, system design and packaged systems.
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Energy conservation is a very interesting field. With the advances of technology we have items like solar panels for energy generation or water heating, battery technology for energy storage and new forms of lighting like LED lamps. A recent article on LED lamps caught my attention recently and I thought it would be a good example for comparison to ammonia refrigeration systems.
I often see questions about this and wonder what sort of answer someone is expecting. Almost all industrial refrigeration use ammonia as a refrigerant. Although there is a renewed interest in CO2 refrigeration systems, ammonia is the dominant refrigerant by choice. When compared to any other mechanical refrigeration system the basic fundamentals apply.
When you try to evaluate the cost of operation what do you look for? The total of the monthly utility bill, the cost of energy, or something else? Utility charges are based on rate tariffs. These are the prescribed methods for billing users for the electricity and natural gas they consume.
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Ammonia refrigeration systems are complex by their very nature. A system can be comprised of a mixture of various manufacturers equipment such as evaporators, compressors, control valves, condensers, and vessels. Secondly, you can have various forms of each of these components. Screws or reciprocating compressors. Evaporative or shell & tube condensers. Flooded, direct expansion, or liquid overfeed coil circuiting.
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By now many of the States in the upper midwest have experienced very cold weather. As some have found, winter time presents some occasional challenges for starting or operating an ammonia refrigeration system.
Since the advent of the mandated Process Safety Management program (PSM) the industrial refrigeration sector has been faced with attempts to maintain lower refrigerant charges (re: inventories of refrigerant used in the system). To date, most of the efforts expended focus on keeping the ammonia refrigerant charge under 10,000 pounds. To a degree, this has largely centered around minimizing the quantity or use of gravity-flooded air-cooling evaporators or flooded shell and tube heat chillers. While these methods will drastically reduce the total refrigerant charge, other methods can be applicable. These typically involve re-thinking the basic premise for the use of a refrigerant and the application of specific sub-systems that are used in ammonia refrigeration systems.
I often see people interested in heat recovery asking questions about desuperheating. This mode of heat recovery is based on circulating a fluid such as water through a heat exchanger to aid in transferring heat from one location to another. One of the major issues with utilizing the superheat of the discharge gas from a refrigeration systems is; there is not a lot of available heat! The available superheat in the discharge gas from a compressor is only a small percentage of the the total available heat energy.
In the final entry on this series, the application of hand expansion valves (HEV) to liquid overfeed systems will be discussed. The application of HEV’s in this type of system somewhat differs from those of the prior discussions. When selecting HEV’s for the evaporators where liquid overfeed is being utilized the hand expansion valves take on a secondary function, which may not be obvious at first glance.
In this entry a unique application for hand expansion valves (HEV) is discussed. Many vessels in industrial refrigeration systems have what we call “float columns”. These float columns usually have mechanical float switches which actuate on predetermined liquid levels within the vessel. It is also common to find capacitance type level probes installed in the float columns to monitor liquid level in the attached vessel.
In the previous blog entry we discussed the use of hand expansion valves (HEV) maintaining a liquid level in a vessel. In this entry the discussion will center on the HEV being utilized as an expansion device to an evaporator being fed with liquid from a controlled-pressure receiver (CPR).
