HVAC Reliability
Equipment has become highly reliable; however, in designing a critical
application such as NYI's Wall Street Facility, it must be assumed that all equipment will fail.
All systems have been designed with redundancy to provide full cooling
continuously. The degree of redundancy should be weighted against the
consequences of equipment downtime.
A minimum of N+1 redundancy is utilized but future expansion and the degree of
backup required have been considered.
HVAC systems currently in use have met the specific design requirements
including:
- High sensible cooling capacity
- Cool, heat, humidity and dehumidify
- Filtration EU4 and above
- Full microprocessor control
- Low noise levels
- High reliability
- Built in redundancy with multiple circuits
Precision Air Distribution of HVAC equipment normally has 2
airflow options - Downflow and Upflow:
Downflow systems are preferable and more common for the following reasons:
- Air is returned through the top of the unit and supplied out the bottom
into a raised floor plenum permitting higher air quantities without disturbing
the occupants.
- Perforated floor outlets can be easily moved giving flexibility in room
layout and close matching of the load.
- The units themselves also form part of the floor grid and can also be
easily moved.
- NYI's Wall Street Facility Internet facilities may have a room load up to
1400 W/m2 without any expansion.
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 Precise Air Conditioning Pictorial, Wall Street facility |
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Water / Glycol systems are used particularly when there is a possiblity outside ambient in
winter drops below freezing, threatening year-round operation. (It's not
uncommon for temperatures to approach the freezing during New York's winter
months). NYI's glycol system consists of an indoor evaporator and condenser and
an outdoor drycooler. These systems have the added advantages that they are
easy to install and also have a free cooling option when low ambient conditions
prevail.
Temperature and Humidity: In comfort applications, latent cooling is
greater due to the contribution of the higher number of people and additional
ventilation air; the sensible cooling is relatively low and typically in the
range 60-70% of the total load. In precision air conditioning applications, the
heat generated is mostly dry heat and the moisture due to people and outside
air is very low, resulting in sensible heat ratios in the range of 85-95%. For
this reason precision air conditioning equipment must be selected to provide
cooling at that same ratio. Standard comfort air conditioners cannot properly
condition the room. They will dehumidify excessively causing low moisture
levels and excessive humidification requirements, which in turn wastes energy
and causes additional maintenance issues. |
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