Abstract
A variety of greenhouse gas reduction scenarios have been proposed around the world to ensure sustainable developments and strengthen the global response to the climate change. To cope with this, it is urgently needed to reduce the amount of energy used for the heating, ventilating, air conditioning, and refrigerating (HVAC&R) systems in large buildings. This study discusses the reduction of cooling energy in large office buildings through the minimization of changes in components and equipment, such as heat source equipment and pumps, changes in the layout and operating methods of chilled water circulation pumps, and changes in the temperatures of chilled and condenser water. To do this, this study targeted an entire cooling system consisting of a hydronic system, a chiller, and a cooling tower, and conducted a quantitative analysis of the energy consumption and of the reduction achieved through a change in the pumping system type in the cooling system and a change in the Korean standard design and temperature of chiller and cooling tower via EnergyPlus simulations. The simulation results showed a cooling energy reduction of 103.2 MWh/yr, around 15.7%, where the primary constant-speed system (Case A) was changed to a primary variable-speed pump (Case B) in the configuration with a chilled water circulation pump. To reduce the cooling energy further, annually 142.3 MWh, around 21.7%, Case C in this study changed the outlet temperature of the chiller and temperature difference from 7 °C, 5 K to 9 °C, 9 K. Finally, when applying a change in the condenser water production temperature from 32 to 23.9 °C in accordance with ASHRAE Standard 90.1 for Case D, a cooling energy saving of 182.4 MWh/yr was observed, which is about 27.8%.
Highlights
The carbon emission from the building sector accounts for 32.7% of the greenhouse gas emitted in South Korea [2]
The energy consumption due to electrification has continued in large-size buildings in South Korea
The heating, ventilating, air conditioning, and refrigerating (HVAC&R) system accounts for 55% of all energy consumption, out of which, around 21.7% is consumed by cooling energy [3]
Summary
The Intergovernmental Panel on Climate Change (IPCC) proposes various greenhouse gas reduction scenarios for limiting the increase of global temperature to 1.5 ◦ C above pre-industrial levels. For the design and selection of piping in South Korea, the safety factor is reflected in all stages without an accurate calculation criteria for the calculation of piping size and the capacity of heat source equipment from the maximum load calculation stage, which is based on the normal specifications set by the Ministry of Land, Infrastructure, and Transport (MOLIT). The reason for the excessive capacity calculation of heat source equipment was because of designers trying to avoid the complaints from occupiers due to the lack of capacity and not wanting to spend time running simulations to get the right design This made the heat source capacity oversized in the end, leading to the reduction in idle areas in buildings as a result of the increase in mechanical room size, the increase in building’s initial investment cost, and increase in operating cost due to the need for energy efficiency [11]. Because the cooling capacity of the chiller changes variably depending on the chilled water outlet temperature supplied from the evaporator in the chiller and cooling tower outlet temperature introduced to the condenser, when increasing the temperature difference of normal design condition values in the current chiller and cooling tower, an effect of a reduction in the pump’s transport energy and a reduction in piping size due to changes in flow can be expected
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