Hot Water Heating Coils For Evaporative Air Conditioners |
The inclusion of a hot water heating coil in evaporative air conditioning systems requires careful design to ensure the summer performance of the system is not adversely effected.
Systems are often run at two speeds and heating function is usually required at low speed only to keep the running cost and heat loads reasonable. Exceptions to this are possible like where the system provides makeup air for exhaust systems such as in kitchens. It is important to clarify how the system is intended to be run before the coil is produced.
Being full fresh air systems running costs can still be high, and air off temperatures are usually kept modest. A typical Melbourne application may raise the air from 5 to 22 deg c. Low speed is typically 50% to 60% of high speed.
Air leaving the outlet of these units is usually at a high velocity of up to 10 m/s and fan static ability is often fairly low. A large transition to the heating coil is usually required to get the face velocity down below 4 m/s so that high speed operation produces acceptable air pressure drops. The actual figure will depend on ductwork resistance and available static, but a limit of 30 to 40 Pa at high speed should be adopted if no figure nominated from the customer. If room for a suitably sized coil is not available a bypass damper around the heating coils can be an answer.
The resulting design usually runs at 3.5- 3.8 m/s on high speed with a 315- 472 fins per meter, 1 row coil to give the desired air temperature rise at low speed. Sometimes calculations need to be redone a number of times adjusting size and fins until a suitable solution is found. Both high and low speed air pressure drops are provided to the customer, shown on the schedule as separate designs.