COVID-19 | CIBSE GUIDANCE Cushman and Wakefield has compiled a checklist for assessing the physical condition of chillers Recommended actions are broadly classified under the headings of natural and mechanical ventilation. This article will look at guidance for the latter. Mechanical ventilation CIBSE recommends that buildings with mechanical ventilation extend operation times, with nominal ventilation being established two hours before and after building usage time. In demand-control systems, CO2 setpoints should be set to 400ppm to increase delivery of outside air, says CIBSE, which adds that ventilation should be kept on 24/7, with lower ventilation rates when people are absent. Where there is humidity control, relative humidity should be set above 40%. Heat-recovery systems should not pose an increased risk if supply and extract streams are completely physically separated, such as twin coil units or plate heat exchangers, although CIBSE recommends an inspection in case there are any leaks that might lead to transfer of air from discharge to intake duct. For thermal wheels (or rotary heat exchangers), CIBSE says there may be a risk of air leakage and moisture transfer between supply and exhaust air streams. A higher pressure on the extract side of the thermal wheel can cause air leakage to the supply flow, particularly in poor installations, so CIBSE recommends that the thermal wheel be bypassed. If it cant be, the rotor should be turned off and the ventilation rates increased as much as reasonably possible. The heat-recovery equipment should be inspected, says CIBSE, and the pressure difference measured and, if necessary, corrected by an appropriately trained technician, using dampers or other arrangements. Workers should adopt usual safety procedures when working on thermal wheels. CIBSE and others recommend stopping central recirculation during the Covid-19 outbreak, by closing dampers via the BMS. While bypassing recirculation may impact the buildings heating or cooling capacity, CIBSE says it was more important to reduce contamination risk and protect public health than to guarantee thermal comfort, and recommends relaxing dress codes. Even if air handling units and recirculation sections had return air filters, it is not a reason to keep recirculation dampers open, as these do not normally filter out particles with viruses effectively because they CHECKING CHILLERS AFTER LOCKDOWN Property services company Cushman & Wakefield has published a guide to reopening buildings, which includes a checklist for assessing the physical condition of equipment and services. This has advice for chillers. Air-cooled chillers n Clean condenser coils and check for leaks and corrosion n Check controls and safety circuits for proper operation n Condenser fans should be cleaned; bearings need to be checked for wear, and lubricated; belts and couplings need to be examined, and tightness checked and adjusted n The electrical disconnect and contactor needs to be inspected for tightness and no pitting n Compressor oil should be tested for acid n Check oil filter and change if needed n Check piping and compressor for any signs of leaks and test refrigerant pressures n Run a general system test to check for unusual noises, odours, and measure supply/ return temperatures and system pressures as needed. Water-cooled chillers n Check quality of condenser and chilled water chemical levels n Check condition of condenser water tubes, and clean if needed n Check refrigerant levels n Check refrigerant purge unit n Check oil heater n Check oil levels n Inspect motors and starters n Run a general system test to check for unusual noises, odours, and measure supply/return temperatures on both condenser and chilled water and system pressures as needed. 38 June 2020 www.cibsejournal.com CIBSE June 2020 pp37-39 Covid aircon.indd 38 22/05/2020 17:48