Page 193 - Boiler plant and distribution system optimization manual

178 Boiler Plant and Distribution System Optimization Manual

Description Table 10.7—Heat Pumps can introduce high efficien-
Heat pumps have high efficiencies when cies when combined with other technologies.
measured against engines, boilers and turbines. In
the example below theh heat pump can bring the
apparent efficiency of a boiler up to 128% using
waste heat or low pressure steam available from
a boiler plant or they can be used to augment old
steam systems with air source heat pumps.
Waste heat can be put to work at a higher
temperature by the use of heat pumps. One sys-
tem design circulated 150°F water from a waste
heat recovery system throughout a plant using
heat pumps to raise the water temperature for lo-
cal heating and process demands.
Table 10.8—The Coefficient of performance (COP) of
The key to how this operates is in the term:
Heat Pumps has the potential to raise the efficiency
Coefficient of Performance (COP), a measure of
of heating systems to over 100%.
the ratio of energy output to energy input. Some
heat pump units have a COP of over 5 which
means the energy to operate them is only about
20% of the energy gained. See Table 10.6 and Fig-
ure 10.78.

Advantages/Disadvantages
First cost, operation and maintenance ex-
penses involved. It is a good way to recover low
grade waste heat.

2. CONDENSING FURNACES,
Table 10.6—Heat Pumps can raise efficiencies sig- WATER HEATERS & BOILERS
nificantly when combined with low grade waste heat
from engines, boilers and turbines. Cost
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High
Comparing Efficiencies of Available Heat Sources
Heat Efficiency
Potential Savings
Heat pump CoP 4 128%
High
Condensing Boiler 95%
Coal fired boiler 83% - 90%
Description
Oil fired boiler 84% - 89%
A greater percentage of the waste energy in
Gas fired boiler 84% – 86%
the exit flue gas stream is in the form of super-
Gas Turbine ~50%
heated steam formed from the combustion of hy-
Diesel ~40% - 50%
drogen in the fuel and other moisture. For every
pound of hydrogen that is burned with the fuel,
Comparing Efficiencies Electrical Sources
vapor carrying with it a great deal of energy. It is
Electrical Efficiency
difficult to recover the latent heat from this vapor
Combined Cycle Gas 50%
without dropping the flue gas temperature below
Diesel Generator sets 30% - 40%
the acid dew point temperature (Figure 10.78 and
Gas Turbine 25% - 40%
Figure 10.79). The acid dew point temperature is
Generating Station 32%
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