1. A note from Geoff Alder… I have posted this file for RACA readers who have been following the “Our Industry” series on the pressure enthalpy diagram. In the RACA March 2007 issue, we discussed heat pumps. I invited interested readers to visit my Website to download this file, which is intended to explain a common arrangement of change-over system as may be used for heat pump application. The graphics have been kept very basic to permit operation on any version (I hope)! of PowerPoint.

2. Pilot valve 4-way valve. Here is an example of the valve type we have in mind… Solenoid coil

3. In the animations that follow, ORANGE signifies high pressure hot gas. GREEN signifies low pressure suction vapour. In the animations that follow, ORANGE signifies high pressure hot gas. GREEN signifies low pressure suction vapour.

4. To open our discussion, here is an animation of the pilot valve in operation… These are the small pilot lines. Pilot valve

5. 4-way valve. 4 – WAY VALVE IN OPERATION Incomers from pilot valve. HOT GAS SUCTION

6. Study the next two slides to see the full circuitry of a typical system for summer and winter operation.

7. Cooling being provided Heat is rejected SUMMER OPERATION 4-way valve

8. Heating being provided Cold air is discarded WINTER OPERATION 4-way valve has now been switched. There will be some form of check valve change-over arrangement to alter capillary or restrictor characteristics to match for heating operation.

9. The following is the pressure enthalpy diagram from the article, which is the reason for this presentation.

11. This ends our mini-presentation. I hope you found it useful! View again?