APC 400kW1MW User Manual download pdf (Page 33)

CHAPTER 4 - Fuel Cell Combined Heat and Power Systems

Combined heat and power systems use similar configurations as typical HVAC systems.

However, CHP systems utilize the waste heat produced by the on-site power generation in

order to meet heating and cooling loads with thermally-activated equipment. Data centers are

an ideal application for CHP because they have constant power and cooling loads [1, pp. 73-74;

20, p. 1-6].

The responsibility of a data center’s cooling system is to maintain specific temperature

and humidity requirements of the IT equipment. If the requirements are not met, the reliability of

the IT equipment is reduced [1, p. 22]. All of the power that is supplied to IT equipment is

converted to heat and ejected into the space surrounding the equipment [39, p. 1]. With large

heat gains from IT equipment, it is no surprise that the power required for data center HVAC

systems is anywhere from 40% to 60% of the total power supplied to the facility [40, para 8].

The American Society of Heating, Refrigerating, and Air-Conditioning Engineers

(ASHRAE) Technical Committee 9.9 (TC 9.9) provides recommended design temperatures for

data centers. During the 2009 Annual ASHRAE Winter Conference held in Chicago, the

ASHRAE TC 9.9 decided that the dry bulb temperature range at the server inlets should be

between 65ºF and 80ºF, opposed to the stricter 68ºF to 77°F range they had previously agreed

on. According to the technical session “Dissipated Data Center Heat through Polymer Indirect

Evaporative Coolers” by Keith Dunnavant at the same ASHRAE conference, servers

manufactured by IBM are able to function with supply air temperatures ranging from 60ºF to

90ºF [41]. The ASHRAE TC 9.9 had recommended a relative humidity design level range of

40% to 45% for data centers in the past. However, ASHRAE TC 9.9 is now suggesting that dew

point levels, opposed to relative humidity levels, should be measured instead, falling in the

range of 42ºF to 59ºF. Also at the 2009 Annual ASHRAE Winter Conference, the committee

decided that measuring the dew point is a more accurate measurement for data center facilities.

The supply air and dew point conditions are required year round, day and night [42, p. 1].

Heat recovered from fuel cells in the form of hot water or steam can be used to power

absorption chillers [20, p. 6-1]. The chilled water produced by absorption chillers can be used to

serve computer room air conditioning (CRAC) units in order to condition the data center [1, p.

80]. This application will be discussed later in this chapter. The typical HVAC system applied to

data centers will first be reviewed in order to make comparisons to a fuel cell CHP system.

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APC 400kW1MW User Manual Page 33