Control options

Evaporator

Evaporator

Heat Exchanger Engineering Drawing

cooling and condensing the refrigerant

Fig. 27.16 The safety devices in the refrigerant cycle cooling and condensing the refrigerant

Fig. 27.16 The safety devices in the refrigerant cycle

The heat absorbed by the evaporator and that generated by the compressor are emitted in the condenser. To recover this heat an additional condenser can be connected in parallel, and alternative positions of a three way valve give two options: 'Hot gas diversion' or 'Condensate control'.

Figure 27.18 shows the second condenser fed from a three way diverting valve installed in the hot gas pipe to illustrate hot gas diversion.

Option 1 When the controller transmits a demand for heating (e.g. via the supply air temperature in the air conditioning system), the modulating diverting valve opens the flow to the heat recovery condenser and closes the supply to the other condenser. If not all the heat recovered is required, the remainder is dissipated via the second condenser.

Fig. 27.18

Figure 27.19 shows the connections for condensate control with the three way value positioned in the liquid pipe.

Condensate Symbol
Fig. 27.19

Option 2 The entire refrigerant flow is normally directed through the valve (see Fig. 27.19). The three-way liquid valve opens the condensate pipe of the heat recovery condenser and closes the pipe of the second condenser when the heat recovery condenser has to emit effective heat. This condenser then releases all condensate thus making its heat exchange surface free for condensation of fresh hot gas. At the same time, the second condenser is filled with liquid thus making its exchange surface inactive. When the demand for effective heat decreases, the process is reversed.

The following examples show how the two options have been applied in a swimming pool/ice rink and a covered shopping complex.

The system shown in Fig. 27.20 relates to an air conditioning system in an indoor swimming pool combined with a low temperature refrigeration system for an ice rink. It is designed on the principle of the schematic in Fig. 27.18 (hot gas diversion) in order to provide a fast response time of the supply air control.

Indoor swimming pools normally require large quantities of heat and have high relative humidity. If cold outside air is mixed with the humid return air,

Kindergarten Printable Worksheet

1 Control valve

2 Expansion valve

3 Evaporator

4 Compressor

5 Heat recovery condenser

6 Outside condenser

1 Control valve

2 Expansion valve

3 Evaporator

4 Compressor

5 Heat recovery condenser

6 Outside condenser

Fig. 27.20 Indoor swimming pool/ice rink condensation results. To avoid this, the outside air is preheated by a heat recovery condenser (5).

Systems installed in enclosed shopping complexes have the following characteristics:

—large heat demand for air conditioning of shopping street

—large heat output from refrigerated cabinets.

Evaporator Symbol Engineering Drawing

1 Control valve 4 Compressor

2 Expansion valve 5 Heat recovery condenser

3 Evaporator 6 Outside condenser

Fig. 27.21 Air conditioning and refrigeration system in an enclosed shopping complex

1 Control valve 4 Compressor

2 Expansion valve 5 Heat recovery condenser

3 Evaporator 6 Outside condenser

Fig. 27.21 Air conditioning and refrigeration system in an enclosed shopping complex

The two condensers in the system illustrated are connected in series. The heat recovery condenser (5) can be switched off completely in summer. In winter, spring and autumn it is used to pre-heat the outside in accordance with demand.

Figure 27.22 shows a simplified schematic of the refrigeration cycle.

Expansion Valve Symbol

1 Control valve 4 Compressor

2 Expansion valve 5 Heat recovery condenser

3 Evaporator 6 Outside condenser

Fig. 27.22 Refrigeration cycle of the shopping complex (simplified)

1 Control valve 4 Compressor

2 Expansion valve 5 Heat recovery condenser

3 Evaporator 6 Outside condenser

Fig. 27.22 Refrigeration cycle of the shopping complex (simplified)

The authors wish to express their thanks for the assistance given and permission to include examples of applications engineered by Staefa Control System Ltd, Hawthorne Road, Staines, Middlesex.

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Responses

  • katie
    How much freo flows through an expansion valve?
    9 years ago
  • Felix
    How to draw a fig of refrigeration system?
    8 years ago
  • Jensen
    How to indicate expansion valve indicate in engg. drawing?
    8 years ago

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