Project
Massmart / Makro are one of the leading companies in South Africa that are trying very hard to reduce carbon emissions and reduce global warming by using natural refrigerants , and gladly accepted the challenge on this project .
With the clever design of the chillers / packs , gas coolers and with CO 2
/ water-ethylene glycol heat exchangers , the thermal storage system produces -7 degree C water / glycol at night for ice production , and + 7 degree C water for daytime use on the HVAC system .
Due to this design , ACS managed to produce favourable electrical energy savings for the site with all HVAC aspects , and refrigeration elements in operation – including free water heating for domestic use and the winter space heating needs .
HVAC system and installation The heart of the HVAC , refrigeration and plumbing installations ’ equipment are located at the back of the store in dedicated plant rooms or exposed to the elements as required .
The HVAC system is a traditional Makro ice thermal storage system of two large vertical steel tanks that use spherical nodules that are frozen at night when the utility rates offered to the client are lower than daytime rates . This method shifts the energy demand to nighttime thus significantly reducing energy costs . The water / ethylene glycol solution is circulated through the ice tanks and CO 2
/ ethylene glycol heat exchangers , which enable the nodules to freeze at -7 ° C .
The HVAC design philosophy is to use ice storage as much as possible and only use the chillers when the demand requires them to assist with the cooling load . On this project the chilling is provided by four South African built refrigeration packs / chillers using Bitzer reciprocating CO 2 compressors with parallel compression - generating the ability to offer low and medium temperatures for the refrigeration aspects .
It must be noted that this is a transcritical CO 2 operation which uses high pressure refrigerant that requires gas cooling . The benefit is that high water temperatures are also possible to gain for domestic water and space winter purposes . This improves the COP and overall operating energy costs , because no electrical elements are used to produce any hot water in the building .
The four packs are installed inside a purpose-built plant room and the four hybrid gas coolers or condensers are air cooled units placed on the roof above the plant room .
Traditional air handling units ( AHUs ) with EC plug fans , chilled water-cooling coils and hot water heating coils are used to condition the internal spaces for summer and winter .
Fabric ducting with appropriately designed diffuser nozzles or orifices have been used as much as possible to supply conditioned air to the internal spaces . This being more cost effective for this application type than traditional sheet metal ducting and diffusers .
HVAC and refrigeration dry coolers with ice tanks in background as well as the rainwater capture tanks .
The refrigeration pack distribution board .
Steel piping with insulation is used to circulate the chilled solution to all AHUs and fan coil units .
Two chilled water / ethylene glycol pumps as duty and standby are used to circulate the solution in the three modes required , namely ice built , ice only and chiller-assist - thus eliminating the use of secondary pumps .
Similarly , two space heating water pumps are used for the winter heating of the store .
The main trading floor and liquor store are air-conditioned by six AHUs placed at the back of the store on a raised steel
www . refrigerationandaircon . co . za RACA Journal I January 2023 39