To recap on the last chapter, the definition of psychrometrics can be said to be the study of dry air and water vapour mixtures. The only source of cooling on any air conditioning system is the evaporator coil. Therefore, in order to remove heat from the space the heat must be transported in some way to the evaporator and the obvious medium used is the air contained by the room which is recirculated through the evaporator coil by the fan within the air handling unit.

The Masterclass series of articles have covered a wide range of topics, some related to specialised applications and some to standard components. However, in some instances, the principles behind their selection have not been covered. Therefore, before proceeding further into capacity control and the specific aspects of refrigeration and ac, we will now look at a complete system to summarise the content of certain preceding articles.

In last month's article we reviewed various approaches to capacity control. This month we continue with other approaches to this important aspect of air conditioning products and systems within the category of control, safety and protection devices used in the vapour compression cycle. We also introduce the study of psychrometrics.

Last month completed our review of compressor lubrication. We now move on the subject of Capacity Control - matching system capacity to varying load conditions.

In the last article we completed our study of low ambient control methods. This month we will concentrate on compressor protection devices with the emphasis on lubrication and its associated control devices for system protection.

In last month's article we continued with our study of low ambient control methods under the current category of our review of Control, Safety & Protection Devices used in the Vapour Compression Cycle in which we covered plant room damper control, multiple fan and fan speed control. This month we complete this element by looking at Head Pressure Control of Water Cooled Systems.

In the last article we looked at low ambient control for air and water-cooled systems. We now continue our study of the various means of providing low ambient control for single and multiple fan condensers on air-cooled systems.

In this month's article we continue our study of low ambient control methods for air and water cooled systems.

In the last article we continued our study of control, safety and protection devices used in the vapour compression cycle by covering the low pressure and high pressure cut-out switches. This month we move on to low ambient control.

In the last article we started a study of control and safety devices used in the vapour compression cycle by covering the thermostatic switch and the low pressure cut-out. This month we continue with the application of the low pressure cutout and move on to the high pressure cutout and other devices.

The last article covered liquid refrigerant receivers. The containment of refrigerant in vessels and refrigerant lines demands that safety be given due consideration to eliminate risk to persons due to refrigerant release or explosion and to minimise refrigerant losses thereby avoiding environmental damage and financial loss associated with replacement. This month we review various methods to meet the aforementioned requirements.

In the last article we looked at shell and tube water chillers and other types of water chiller evaporators. This month we conclude our study of the major refrigeration components by looking at Baudelot coolers and liquid refrigerant receivers.

In the last article we studied the construction, testing and protection of shell and tube evaporators. Part 16 continues with information on shell and tube water chillers and other types of water chiller evaporators

In the last article we completed our review of BPHE’s. This month we move on to direct expansion water to refrigerant evaporators. These are often referred to as shell & tube evaporators or chillers.

In the last article we studied fin and tube evaporators. A study of the increasingly popular brazed plate heat exchanger (BPHE) as an evaporator now follows. It is interesting to note that BPHEs are also extensively applied as condensers in order to reject heat energy from refrigerant to water, particularly in reverse cycle heat pump applications.

In the last article we completed our review of thermostatic expansion valves. The following continues our study of expansion devices and distributors.

In part 10, capillary tubes, restrictor expansion devices and the thermostatic expansion valve (TEV) were studied. In this month’s article we continue our study of the range of expansion devices available.

IN PART 8 and 9, the methods of heat rejection utilising air cooled and water cooled condensers were studied including the fundamentals of cooling towers. Following the flow of refrigerant around the vapour compression cycle circuit now takes us to the expansion device.

This month we continue our study of air-cooled condensers, looking at various forms of control, materials, unit selection, system design and energy conservation.

Over the last three months we have studied various compressor types. Following compression, the high-pressure refrigerant vapour is passed to the condenser where the latent heat of condensation is rejected thus returning the refrigerant to liquid form. As this step follows compression, a study of condensers now follows.

In parts 5 and 6 we studied reciprocating and scroll compressors. Rotary vane, screw and centrifugal compressors are covered here in part 7.

This month we continue our study of compressors and the alternatives to the reciprocating compressor.

Energy

Energy is normally defined as the ability to perform work and is consists of:

Mike Creamer of Business Edge revisits his Masterclass series of articles, updating and adding to the information which proved so useful to readers when the series was first published ten years ago. In this reincarnation, the series will cover both air conditioning and refrigeration and serve as an ongoing source of technical reference for experienced personnel as well as providing a solid educational grounding for newcomers to our industry.

In the last article we looked at the vapour compression cycle and the behaviour of the recirculating refrigerant (R22) as it passes through the evaporator, compressor and condenser. In this month’s article we continue with the expansion device and move on to describe the absorption refrigeration cycle.

In the last article we looked at refrigeration cycles. We shall now move on to the key components of the vapour compression cycle starting with the heart of the system – the compressor.

THE PRIMARY refrigerant used in air conditioning for decades is R22 (HCFC22). Whilst its ozone depletion potential (0.05) is much less than other less friendly earlier refrigerants (ODP 1.0), it is still necessary to phase this refrigerant out. Accordingly, the majority of new air conditioning systems now use R410a. However, there are still many systems operating on R22 and this will be the case for some years to come.