Upgrade the Paint Booth area to include a Dry Off cooler and Primer cooler area as the products were suffering from inconsistency in product quality. Neither of the latter were under temperature or humidity control. Temperature required 240C +/- 20C, RH 65% +/-5%.
Each zone area of the plant needs to be able to be controlled both independently or simultaneously.
Included would be an upgrade to the existing chiller and upgrade of a heating system addition of gas fired boiler to make up a shortfall.
Initial design concept started in 2018 with a minimum system requirement of:
- 700kW cooling @ 60C supply.
- 380kW heating with additional 500kW @ 450C supply.
Efficiency was to be an important consideration as the existing chiller had heat recovery incorporated in its design. However, whilst in theory that sounds good when the client wants the ability to have temperature and humidity control either separately around the plant or simultaneously heat recovery has limitations as you can only get recovered heat when the chiller is running in cooling. A lack of understanding of the intricacy of the refrigeration cycle has lead to many failures when trying to incorporate heat recovery or heat pump technology.
When the chiller is cooling the heat absorbed must be rejected. As can be seen in the diagram a solenoid is either open or closed so heat is either rejected to atmosphere through condenser coils or rejected into the water through the heat recovery condenser which is why the additional boiler is required if there is a need for heating when there is no cooling load. The diagram is only showing heat recovery on one circuit which satisfies the current system but doesn’t address the new requirements.
A change of thinking is required to be able to supply heating only, cooling only or heating and cooling at the same time. This plant also needs to account for a change in the load in the different spray booths or coolers where you may require more heating than cooling or vice versa. Because the project only requires 450C supply in heating mode this is a very low temperature for a boiler and suits a recovery/heat pump application. When plant room space is at a premium it is not as easy to supply a heat pump and a chiller separately. But in that situation if a chiller only is required the heat pump is idle or if heating is required the chiller is idle.
The ideal is to have both heat pump principle and chiller combined in the one platform. Then it would be possible to eliminate the requirement for the boiler. This then throws in the control logic that needs to be developed to satisfy the individual plant control or simultaneous requirement but more importantly be able to handle the changing demands on a chiller/heat pump as during mode changes the refrigerant could end up in the wrong part of the system leading to failures and oil recovery can become an issue. Then in winter when cooling will only be required as part of the dehumidification the heat pump will need to have the ability to defrost if required. Particularly if it is in full heating mode. In this situation defrost must be able to be handled without impacting on system performance.
To enable system stability adding additional water volume will allow small fluctuations during mode changes without affecting the temperature stability.
With efficiency being the client’s driver a quick example of the difference:
- Gas boiler efficiency = 90%
- Chiller only = 280%
- 4 pipe system (heat pump/chiller) = 610%
- Operating hours = 8760
- Utilisation = 60%
- Cooling = 690kW
- 50% heat recovery = 435kW
- Power input = 200kW
- 500kW boiler @83% system efficiency = 605kWh
- 2 * CMAF 140 4 pipe systems (Heat Pump/Chiller)
- Cooling 894kW
- Heating 703kW
- Power input 322kW
This equates to a 27% saving using 2 heat pump/chiller systems on the new system incorporating the demand of the Primer Cooler and Dry Off Cooler.
The biggest challenge was during commissioning ensuring the airflows were correct on the additional cooling along with balancing water flow rates. Once these were set and modifications to the fan performances were set. The careful time spent configuring the control philosophy in each mode of operation required: Cooling only, heating only, 50% heating,50% cooling, 50% defrost, Heating priority, Cooling priority, Maximum heating capacity, Maximum cooling capacity.