www . refrigerationandaircon . co . za RACA Journal I August 2023 31
Feature summer versus winter conditions , location , the current plant and HVAC infrastructure .
“ As an example , you can consider a 1 000kw plant , chilled water in an office park application , nine hours of operation using a 1 000kw chiller drawing 400kw ( air-cooled chiller ). We can consider seven Calmac tanks 500kw / hours of storage per tank for a total of 3 500kw stored energy , which would result in a reduction with only 550kw of cooling required from the chiller ( half of the chiller size required ) with partial storage of seven Calmac tanks ,” explains Muller .
He adds that return on investment ( ROI ) is the most important element : noting that at the current electrical tariffs the ROI in the case of Calmac thermal storage is around four to six years , “ which is very quick considering the electrical savings for the client and convenience of having cooling during load shedding ”.
He explains that the essential element of the Calmac Ice Bank System is a modular , insulated , polyethylene tank containing a spiral wound plastic tube heat exchanger surrounded with water . The tank is available in many sizes ranging from 160 to 1 760kW-hours . At night , water containing 25 % ethylene glycol is cooled by a chiller and is circulated through the heat exchanger , extracting heat until eventually 95 % of the water in the tank is frozen solid . The ice is built uniformly throughout the tank by the patented temperature averaging effect of closely spaced counterflow heat exchanger tubes . Water does not become surrounded by ice during the freezing process and can move freely as ice forms , preventing damage to the tank . Calmac tanks are virtually maintenance free and have no moving parts , resulting in extended life span of the tanks .
“ Thermal storage assists clients with large reductions in the capital cost of chillers – so smaller chillers may suffice . Other benefits include : lower maintenance costs with smaller chillers and tanks ; large reductions in running costs ; longer life span on thermal storage plants . Thermal storage allows clients to build thermal energy at night when electricity is 25-50 % of the cost the next day , thereby reducing electrical loads during peak times . By having additional cooling in winter there is further savings during winter , autumn , and spring months ,” says Muller .
HOW DO YOU DETERMINE IF THERMAL STORAGE IS RIGHT FOR A BUILDING ? Ngonidzashe Kundhlande , development engineer at Baltimore Aircoil Company SA , says : “ Traditionally , ice thermal storage has been considered as a way to shave the peak load off a building and shift the load to lower load periods of the day and periods where off-peak electricity rates would apply . So , in essence ice thermal storage reduces energy costs , minimises peak electrical demand , and lowers system costs . By producing low process fluid temperature during off-peak times , this environmentally friendly cooling solution reduces energy consumption and greenhouse gas emissions .
“ South Africa finds herself with the low energy security situation which will most likely persist for the foreseeable future , and it is incumbent on everyone to do their bit in reducing energy consumption and find viable alternatives to how things have traditionally been done . We , at Baltimore Aircoil Company , believe that the ice thermal storage provides a unique opportunity to contribute to this as all the benefits mentioned above would apply and should be considered as one of the possible solutions ,” says Kundhlande .
He notes that the largest portion of a building ’ s energy consumption goes to cooling , and ice storage will not only help by reducing peak energy demand , thereby reducing pressure on the grid , but also provide the much-needed cooling during loadshedding periods at a much lower cost than what is being seen at present .
“ Currently , back-up systems ( diesel generators ) need to be sized to provide enough energy to power the whole cooling system , whereas ice thermal storage affords you the opportunity to build and store ice during the ‘ grid up-time ’ and then melt that ice during a loadshedding period . During the melt cycle , the energy users on the cooling system could be the chilled water pumps and AHUs with the biggest energy user , the chiller , being off completely .”
By considering ice thermal storage one could alter the energy usage profile of a building in a way that profoundly affects the energy costs , impact on South Africa ’ s fragile grid , and impact on the environment . RACA
REFERENCES :
1 . ASHRAE Research Paper-1607 : Design and Utilization of Thermal Energy Storage to Increase the Ability of Power Systems to Support Renewable Energy Resources , January 2018 . 2 . Western Cooling Efficiency Center at University of California Davis 3 . Source : Calmac . com https :// archive . nytimes . com / www . nytimes . com / 2017 / 06 / 03 / business / energy-environment / biggest-batteries . html
www . refrigerationandaircon . co . za RACA Journal I August 2023 31