The client had previously installed several free-cooling systems to test the viability of using free cooling to augment existing air conditioning units. Due to a variety of factors, the client came to the conclusion that free cooling systems did not work. Based on the information we were able to obtain, the negative results appeared to be related to poor execution of the test program rather than a failure of the free cooling concept. To overcome the initial resistance to free cooling, we presented detailed calculations to predict significant energy savings and offered to run a fully monitored year-long trial to prove our claims. The client agreed, provided we agreed to remove our equipment if we failed to deliver on our projections.
The site selected for the trial contained a 3kW heat load being cooled by a 2.5 ton wall-mount packaged AC unit widely used in telecom shelters. This unit was equipped with an optional economiser. We supplied and installed a FC300 free cooling system with gravity pressure relief damper. We replaced the existing thermostat with an FC10 intelligent control system which operated the modulating free-cooling fan as well as the compressor, evaporator fan and heater in the AC unit. The room set point was not changed, but we disabled the economiser in the existing packaged AC unit. For data collection we used the FC10 onboard temperature logging feature, as well as power monitoring equipment to collect electrical consumption data.
The predicted energy saving from the HVAC unit was 88%, but the observed energy reduction was 80% which translated into a 35% overall site energy reduction. The difference was due to the economiser, which was not taken into account for the predicted calculations. Based on the prevailing energy costs at the time, the payback was estimated under 2.5 years. In addition to significant OPEX savings, during free cooling operations the site operated at close to flat line steady state in terms of temperature profile and power consumption. It was estimated the free cooling fan eliminated approximately 16,000 compressor cycles per year, thereby extending the service life of this equipment. The free cooling mode also lowered the street noise level from the site. The advanced controls also provided alarm functionality over SNMP, data logging and full remote monitoring. This field trial was deemed a success and many more sites were subsequently retrofitted with free-cooling units.
overall site energy reduction.
estimated compressor cycles per year.