Methods of Refrigeration Term Paper
- Length: 5 pages
- Subject: Energy
- Type: Term Paper
- Paper: #93009864
Excerpt from Term Paper :
Refrigeration in American Craft Brewing Industry
The purpose of this study is to examine the use and operation of various refrigeration systems used in the American Craft Brewing industry. This includes such as glycol chillers, walk-in evaporative coolers and refrigerated dispensing systems including how the systems work and their function in the brewing process.
Condenser cooling uses air or water and it is reported that each of the methods are characterized by both strengths as well as weaknesses. Air-cooled compressors are reported to potentially "lose significant cooling capacity on a hot day" and this is when the capacity for cooling is most needed. The water-cooled systems are reported to be more efficient in their operation but at the same time to make a requirement of "more maintenance and investment cost." (Prochiller, nd, p.8) Cold box refrigeration systems make provision of cooling for "a small direct-draw box cooler or a large walk-in." (Prochiller, nd, p. 8) The refrigeration is reported to be "either…self-contained with the compressor and condenser mounted on the unit or with a remotely mounted compressor and condenser." (Prochiller, nd, p. 8) When the compressor is mounted remotely the installation is benefited through the removal of the heat source from inside the building or room however, this means that there must be "additional refrigerant piping" which is likely to result in a higher cost. (Prochiller, nd, p. 8) Glycol use in process chiller applications is reported in the work of King (nd) to be a subject that is challenging at best. The types of glycols used most commonly in Chiller applications are Ethylene Glycol (E.G.) and Propylene Glycol (P.G.) The following table relates the primary characteristics of each of these types of glycol including the "freeze point depression, heat transfer efficiency, viscosity, flammability, chemical oxygen demand, biograding, carcinogenic, toxic, and skin" irritant properties. (King, nd, p. 5)
Property Ethylene Glycol Propylene Glycol Comments
Freeze point depression More effective Less Effective more antifreeze is needed of propylene glycol to achieve the same freeze point.
Heat transfer efficiency less Better Ethylene glycol cannot carry as much heat as can propylene glycol. More fluid needs to be circulated to transfer the same amount of energy. Pumps volume increased.
Viscosity Lower higher Propylene glycol increases major head loss in the systems. Pump head increased
Chemical oxygen demand Low Higher
Biodegrading Degrades in needs more than in 10-30 days 20 to 30 days to degrade
Carcinogenic No A carcinogen is any substance or agent that promotes cancer.
Toxic high level of acute lower level of acute Ethylene glycol should never
When taken orally be used in any drinking water
Targets the kidneys or food processing systems
Skin Irritant Low Propylene glycol is used in small amounts in cosmetics
Source: King (nd)
It is reported that a debate exists as to what type of glycol to use in process chiller applications and according to the work of King ( ) the key considerations include: (1) glycol concentration; and (2) environmental considerations. (King, nd, p. 5) According to King the lower the process fluid freeze point needed then the more glycol concentration the system will require. King states that Ethylene Glycol is the best performer and in addition does not require as much volume in order to achieve the level of freeze protection desired. Environmental considerations include the fact that Ethylene Glycol is a toxic material and this means increases in operating costs due to the needs of special training required for handling and disposal of this material. This means that in terms of environmental considerations that Propylene Glycol is the best choice due to the low impact of the material on the environment. The chiller cooling capacity reported by King relates that capacity loss is a necessary considerations since "as the concentration increases heat transfer between the chillers Evaporator slows due to the fact that "glycol is less conductive to heat transfer than water." (nd, p. 5) King reports that the chiller btuh reduction factors are provided in the following table which compared propylene loss factor and ethylene loss factor.
Glycol Type 20% 30% 40% 50% 60%
Propolyne .93 .90 . 87 .83 . 76
Loss factor .
Loss factor .90 .86 .91 .76 .71
Commissioning of glycol chiller systems are such that require a qualified technician and the use of glycol results in more complexity that requires consideration to avoid issues operationally. The service points that need to be considered include the following: (1) hot gas bypass systems; (2) chiller flow safeties; (3) compressor low pressure safeties. (King, nd, p. 6) In the majority of cases it is reported that hot gas regulator valves are factory set for water. This is accomplished by design in order to prevent potential evaporator damage in the event the customer tries to run the process temperature set-point lower than 45 F. without first adding glycol. Since hot gas regulators respond to the compressors suction pressure, they will tend to deploy too soon on glycol systems. When this happens it is reported that the end user generally complains of a lack of capacity of the chiller. Chiller flow safeties are reported to be calibrated for water at the factory. When glycol is added to the process loop, viscosity will change the concentration of the glycol and generally the glycol will change the flow and it is stated that pressure drop across the chillers evaporator which calls for calibration in the field as part of the commissioning process. Generally, the chillers low pressure fault presets will require adjustment and these adjustment will serve as prevention against nuisance low pressure shut downs of the compressor. According to King, Glycol has more weight than does water and the additionally weight may result in increasing costs of energy and open loop systems and as well friction losses are produced by glycol when it moves through the valves, fittings, filters and the straight pipe. Changes in the glycol viscosity occur when process loop temperatures reach "F of the freeze point" and as the slush point is approached glycol process loop friction losses are reported to increase and more pumping power is required. (King, nd, p. 5) Regular testing of fluids results in glycol operating success however, failure to test fluids results in failures in the system and degradation of the glycol inhibitors and it is reported that following inhibitor levels dropping to somewhere around 70% of initial levels what occurs including process system material breakdown including the piping, heat exchangers and pump impellers and this is an accelerating process. Fluid replacement should be conducted every six to eight years. (King, 2009, p. 4)
II. Evaporative Cooler
Evaporative cooler ability and performance is varied and this is reported to be dependent upon the parts that are contained in the cooler. It is reported that the circulating pump, the thermometer, the absorbent wet pad and the cooling fan are the primary components of the cooler unit. The hot air is stated to be drawn into the unit from outside of the unit and it is then reported that the hot air is drawn through a wet pad which results in cooling the air and the cooled air blows through the vents indoors. (Instructables, nd, paraphrased) The primary factor in the cooling result is reported to be the wet pad since one key factor is absorbency and the type of pad used changes the absorbency rates which shift between sixty and ninety percent depending upon the pad's absorbency. Aspen wood pads inside plastic netting is reported as an effective pad for use in the walk-in evaporative cooler and it is generally agreed upon that the thicker the pad the better the pad works. The circulating pump is reported to be something like a radiator in a car and keeps the water moving…