Summary
Heat pump
technology is important for boosting the reduction of CO2 emissions, reducing
primary energy consumption, and increasing the amount of renewable energy used.
The scope of industrial applications is also expected to expand, further
enhancing these effects. Trends introduced in industrial heat pump technology
in Japan include pioneering high-temperature heat pumps, such as CO2
refrigerant transcritical cycle heat pumps for hot water and hot air supply,
reverse Rankine cycle heat pumps for heating and cooling of circulating water,
and steam-generating heat pumps.
Introduction
Heat pump technology is important for reducing CO2 emissions, reducing
primary energy consumption and increasing the amount of renewable energy used.
The scope of industrial applications is also expected to expand, further
enhancing these effects. In particular, the development and spread of
high-temperature heat pumps for hot water supply, heating of circulating hot
water, and hot air and steam generation must be supported. This paper describes
trends in industrial heat pump technology in Japan.
Steam Supply Service in a Factory
At a
company producing cars, auto parts, electrical equipment, food, etc. as shown in
Figure 1, steam is produced in the energy centre, supplied to all areas of the
factory, and used in the manufacturing process.
However, overall energy efficiency is generally low, due to boiler losses,
heat losses from piping, steam leakage losses in traps, and drain recovery
losses.
Reports suggest that total energy efficiency has improved from 26.6 % to
38.7%. Moreover, research has been reported indicating that the most commonly
used steam temperature zone is in the range 55-80oC, and that the most commonly
used steam heat load zone is less than 5 kW.
In addition, many electric heaters are used for these processes for which
temperature control is required.
Distributed Heat Pumps and Heat Recovery
Accordingly, significant energy savings are expected by replacing some
steam infrastructure and electric heaters with low energy efficiency with
distributed high-temperature heat pumps for hot water or hot air supply, heating
of circulating hot water and steam generation. Heat recovery, i.e. the
simultaneous utilization of cooling and heating or the utilization of waste
heat - should be considered as shown in Figure 1.
Hot Water or Hot Air Supply
A CO2 refrigerant transcritical cycle heat pump can generate hot water or
hot air as required.
Figure
2(a) shows the general arrangement and energy flows of the CO2 refrigerant
air-source heat pump supplying hot water, delivering hot water at a temperature
of 90oC and with a heating capacity of 74.0 kW and COP of 4.2.
The compressor is of the screw type. This heat pump has been supplied not
only to Japan but also to South Korea, Taiwan, Indonesia and elsewhere.
Figure 2(b) shows the general arrangement and energy flows of the CO2
refrigerant water source heat pump when used for the supply of hot air, which
can generate hot air at a temperature of 100℃, with a heating capacity of 110 kW
and COP of 3.7.
Heating of Circulating Hot Water
In many industrial processes, hot water cooled by 5 to 10 degrees is
reheated and circulated. If a CO2 transcritical cycle heat pump is applied to
such processes, the COP will often fall. The reverse Rankine cycle, using HFC-
134a refrigerant, is used for heating circulating hot water at 60 to 80℃ and
delivers a high COP.
Figure 3
shows a schematic of a typical application of the reverse Rankine cycle air- or
water-source heat pump with HFC-134a refrigerant. While cooling water-soluble
cutting oil, this heat pump heats the liquid which washes the machined parts,
thus providing simultaneous cooling and heating. Three operating modes ? heating
mode, cooling mode and heating and cooling mode ? are available, using the heat
exchanger between the air and refrigerant in either direction of heat flow, as
required. The total COP in heating and cooling mode reaches 5.
As an example of the effect achieved using these heat pumps, a reduction of
73% in primary energy consumption and 86% in CO2 emissions compared with the
conventional combination of cooling by chiller and heating by boiler steam, has
been reported. At factories producing cars or auto parts, many heat pumps of
this type are starting to be adopted.
Steam Generation
Since an HFC-245fa refrigerant has a critical temperature exceeding 150°C,
a single-stage compression or two-stage compression heat pump can be used for
re-heating circulating hot water at temperature exceeding 80oC, or steam
generation at a temperature exceeding 100oC. The dual cycle, which consists of
an HFC-245fa cycle for the high-temperature side, and another refrigerant
(HFC-134a or HFC-410A) for the low-temperature side, is also efficient.
Figure 4
shows a schematic diagram of two models of a steam-generating heat pump.
The SGH 120 version generates steam initially by heating pressurized water
and evaporating it in a flash tank after leaving the heat pump unit. This model
generates steam at 120℃, with a flow rate of 0.51 t/h and a COP of 3.5 from a
waste hot water input temperature of 65℃.
The SGH165 model generates steam at 165℃. After the heat pump unit
generates steam, the steam compressor increases the steam pressure and
temperature still further. The flow rate of the steam is 0.89 t/h and the COP
reaches 2.5 from a waste hot water temperature of 70℃. The SGH120 model has a
two-stage compressor, and the SGH165 has a single stage compressor.
HFC-245fa is selected as the refrigerant of the SGH120 model, and a mixture
of HFC-245fa and HFC-134a is selected as the refrigerant of the SGH165 model,
considering the capacity per unit refrigerant flow.
Conclusions
The trend in industrial heat pump technology in Japan is towards the
introduction of pioneering high-temperature heat pumps, such as CO2 refrigerant
transcritical cycle heat pumps for hot water and hot air supply, Reverse Rankine
cycle heat pumps for heating and cooling of circulating water and steam
generation heat pumps.
It is important, when intending to apply heat pumps for industrial
applications, carefully to investigate the required final heat condition for
each manufacturing process, in order to identify and quantify energy savings,
economic efficiency, installation space etc. The dissemination of industrial
heat pumps is more difficult than home-use air conditioners since the
manufacturing process is basically a secret. It is important to provide
demonstration installations that clearly show the benefits of heat pumps. It is
believed that industrial heat pumps will penetrate further when the different
requirements for industrial heat pumps are organized and generalized, to some
extent.
Source: IEA Heat Pump Centre Newsletter Vol. 30, No.1, 2012
85 
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