Page 225 - HVAC Pump Handbook

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The Use of Water in HVAC Systems

222 The HVAC World

This annual energy loss in kilowatthours can be used to determine
the additional annual energy consumption of the chillers due to the
balance valves:
annual kWh 3412 average kW/ton
v
Added chiller kWh
12,000
annual kWh average kW/ton
v
(8.16)
3.52
where total annual kWh is for the balance valves, and average kilo-
v
watts per ton is the annual kilowatthour consumption of the chillers
divided by the annual ton-hours of cooling produced by the chillers.
For example, if the annual loss due to balance valves is 100,000
kWh and the average kilowatthours per ton-hour is 0.80, then
100,000 0.80
Added chiller kWh
3.52
22,727 kWh

The total annual loss for the balance valves is therefore 100,000
22,727 kWh, or 122,727 kWh.
The energy loss for the balance valves on hot water systems must
recognize the heating effect of the energy consumed in these valves.
This is done as follows for gas fired boilers. The equivalent fuel per
kilowatt EF/kW in cubic feet is calculated first, and then the net
deduction in percent is developed:

EF 3412 Btu/kW
3
ft gas/kW (8.17)
kW B 1000 Btu/ft 3

where B is boiler efficiency as a decimal. The heating value of nat-

3
ural gas is assumed to be 1000 Btu/ft . Thus, heating effect H in
ef
percent is
3
EF/kW fuel cost (cents/ft ) 100
H % reduction (8.18)
ef overall power cost (cents/kW)
3
Using these equations, with a natural gas cost of $4 per 1000 ft ,or
3
0.4 cents/ft , overall power cost of 6 cents/kW, and a boiler efficiency of
80 percent,
3412
3
EF/kW 4.265 ft /kW
0.8 1000
4.265 0.4 100
H 28.4 percent reduction
ef 6

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