CHILLER RETROFIT | HEAT RECOVERY with a relatively high overall COP. On new, well-insulated buildings with lower supply air/ water temperatures, the heating COP can be 7 or more, reducing operating cost even further. The replacement of these old machines allows for improving their COP to about 4.3 by reducing the logarithmic mean temperature difference (LMTD) between the refrigerant to chilled water and refrigerant to heatrecovery water by about 3.5 fold. This reduces operating costs in summer and winter, justifying the economical upgrade to current refrigeration machine heat-transfer design practices. This lowers the electrical demand, requiring fewer PV panels/battery storage, and their installation becomes viable, enabling the building to be a net yearly exporter of electricity to the grid. Unfortunately, in the event of one winter heat-recovery machine failure, there can be a problem meeting the heating requirement fully during very cold weather. So, during the installation of new, upgraded machines with safer refrigerants, an additional heating heatrecovery condenser on the third machine is suggested, to give standby capability. This additional condenser, however, means that all three heat pumps need only operate at two-thirds capacity to meet the maximum heating demand. Having the series circuitry with the counter-water-flow arrangement, increases their winter COPs by about 4.7 (heating COP 4.7 + [1 motor energy] = 5.7). This energy saving justifies the installation of the extra heating condenser instead of a standby emergency boiler. The installation of only one HWS heat-recovery condenser can, again, cause problems if it fails. Instead of installing an electric/boiler standby heater, the fitting of an additional standby HWS condenser on the Varying the amount of additional cool winter outdoor air from a heat-balance detector controls the loading/unloading of the winter heat pumps and the heat they produce second machine would enable the two HWS condensers to warm the HWS to higher temperatures and provide standby coverage. Heat from lights during morning instead of afternoon cleaning reduces the size of the heated (water) storage vessel required for the early morning preheating of the building. Stored heat is collected from the previous day(s) surpluses, which usually eliminates the need for natural gas boiler(s) or electrical heaters. Varying the amount of additional cool winter outdoor air (more than minimum ventilation air requirement) from a heat-balance detector (thermostat in flow [supply] pipe) controls the loading/unloading of the winter heat pumps and the heat they produce. This extra outdoor air produces a far healthier indoor environment. The CPD article in CIBSE Journal July 2019 shows some environmentally safe replacement refrigerants. One manufacturer is considering a new refrigerant, HFO-1336mzz(E), which eliminates the safety issues present with some replacements. Its safety rating is A1 with zero ozone depletion potential (ODP) and a global warming potential (GWP) of about 32 but it has a low density (about oneseventh of R-410A). The manufacturer is testing a new high-speed about 17,000rpm high-volume, small-screw compressor to address this issue. Preliminary tests on an 18kW unit indicate that, with modification, it is likely to be more efficient and environmentally safer than the R410A it replaces. Breweries, among others, use ammonia with its ultra-low GWP and ODP as their refrigerant . When replacing old machines, engineers should consider the incorporation of two extra heat-recovery condensers, as described previously. This would enable free heating of HWS and general heating from the chillers, which operate throughout the year for product creation. Adding PV solar panels/battery storage reduces operational costs and carbon emissions even further, allowing the facility at times to be, potentially, an exporter of electrical power. CJ JOHN HAMMOND is an energy consulting engineer Trusted Technology Partner Silas Flytkjaer, Head of Strategic Business Development - Commercial www.sav-systems.com 80 September 2019 www.cibsejournal.com CIBSE Sep19 pp79-80 Heat recovery Hammond.indd 80 23/08/2019 15:27