E 503.5.2 Fluid Economizers, Design Capacity
- Systems primarily serving computer rooms in which 100 percent of the expected system cooling load at the dry bulb and wet bulb temperatures in accordance with Table E 503.5.2 is met with water-cooled fluid economizers.
- Systems primarily serving computer rooms in which 100 percent of the expected system cooling load at the dry bulb temperatures listed in Table E 503.5.2 is met with air-cooled fluid economizers.
- Systems where dehumidification requirements are not capable of being met using outdoor air temperatures of 50°F (10°C) dry bulb or 45°F (7°C) wet bulb and where 100 percent of the expected system cooling load at 45°F (7°C) dry bulb or 40°F (4°C) wet bulb is met with water-cooled fluid economizers. [ASHRAE 90.1:184.108.40.206.1]
Units that include an air economizer shall comply with the following:
- Unit controls shall have the mechanical cooling capacity control interlocked with the air economizer controls such that the outdoor air damper is at the 100 percent open position when mechanical cooling is on, and the outdoor air damper does not begin to close to prevent coil freezing due to minimum compressor run time until the leaving air temperature is less than 45°F (7°C).
- DX units with a rated capacity no less than 65 000 Btu/h (18 kW) that control the capacity of the mechanical cooling directly based on occupied space temperature shall have not less than two stages of mechanical cooling capacity.
- Other DX units, including those that control space temperature by modulating the airflow to the space, shall comply with the requirements of Table E 503.5.3. [ASHRAE 90.1:220.127.116.11]
|RATING CAPACITY, Btu/h||MINIMUM NUMBER OF MECHANICAL COOLING STAGES||MINIMUM COMPRESSOR DISPLACEMENT*|
|≥65 000 and <240 000||3||≤35% of full load|
|≥240 000||4||≤25% full load|
For SI units: 1000 British thermal units = 0.293 kW
* For mechanical cooling stage control that does not use variable compressor displacement the percent displacement shall be equivalent to the mechanical cooling capacity reduction evaluated at the full load rating conditions for the compressor.