We are planning to use the rejected heat from oil cooling on our screw compressors to warm a water storage vessel. We currently have a water/glycol circuit doing the cooling through a coil in the condenser. We are proposing to divert this heat to a simple indirect loop within the warm water cylinder to increase the temperature of the water prior to entering the boiler.
The glycol circuit is an 80mm stainless pipe with 7.8l/s flow with a maximum available 310kW of heat. The glycol will enter the heating loop at 41°C, leaving at 31°C.
In the worst case, the water entering the tank at 16l/s will be at 10°C.
Can anyone tell me how to calculate the surface area of the pipe doing the indirect heating to try and get the water to 31°C.
Incidentally, the tank will hold 28,000L and when the oil return temperature is too high the glycol circuit will simply revert back to being cooled in the condenser circuit.
Many thanks in anticipation.