![]() As such, additional chilled water buffer tanks may need to be added on the chilled water system to meet the more stringent loop volume requirements, (i.e., 3,000 gallons). For example, the building chiller may require a loop time of 2 minutes, while the temporary chiller requires a 3-minute loop time if the chilled water flow in the temporary mode of operation is 1,000 gpm, then the minimum loop volume is 2,000 gallons for the permanent chiller and 3,000 gallons for a temporary chiller. ![]() Typically, the loop volume is calculated by multiplying the design chilled water flow with the loop time. To make matters worse, the system is now “deprived” of piping length due to the isolation of the noncritical loads. Based on the chiller type and unit control capabilities, each chiller manufacturer has specific loop volume requirements. Just like the building’s water-cooled chillers require a minimum amount of water volume in the chilled water system, the same applies to temporary chillers - particularly if the temporary chillers use scroll compressors. The onboard controls of the chiller often require a certain system volume (i.e., loop volume) to maintain good chilled water temperature control and ensure compressors are not cycled unnecessarily. The terminal units and other HVAC system components are not shown in the figure nor described in this article. The heating plant serves the AHUs and any terminal units that are provided with a hot water heating coil. The chilled water plant serves the air-handling units (AHUs), various IT rooms, and a data center on the first floor. Hospitals, BSL-4 research laboratories, and data centers are some of the facility types that typically require redundancy and resiliency levels beyond code requirements.įigure 1 shows a riser diagram of a large building (i.e., greater than 200,000-square-foot) that is being served by a water-cooled chilled water plant and a heating plant with high-efficiency condensing boilers. In this scenario, determining what needs to stay operational beyond what is required by code is a balance between cost and the owner’s risk tolerance. However, since code requirements represent a minimum set of performance criteria, it is not unusual for the building owner to ask for increased resiliency. ![]() What exactly constitutes an emergency? To find the answer to this question, one first needs to have a good understanding of the relative code requirements. This discussion is most important, as it will be used by the mechanical engineer to establish the design criteria and associated mode of operation of the building HVAC systems during an emergency. When building owners want their building systems to be designed for resiliency, the discussion between the owner and the engineers typically includes redundancy and temporary HVAC systems that can support all building HVAC systems or portions thereof. ![]()
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