Page 123 - Low Temperature Energy Systems with Applications of Renewable Energy

112 Low-Temperature Energy Systems with Applications of Renewable Energy

air flow-rate), the WLHPS is the most inexpensive investment, 25% lower than the
cost of fancoils; (11) high energy efficiency, so heating costs are 50% lower than in
centralized heat supply systems; and (12) the possibility of combining separate sys-
tems for utilizing the heat of ventilated air and that of waste water into one system.
Therefore, using WLHPS as local units in comparison with fancoils is preferable.
A water-loop circuit receives thermal energy from condensation and yields it to
evaporation in reversible heat pumps that address the thermal loads of different zones
of a building. Heat pumps using a water loop as a heat source have very good effi-
ciency. One important advantage of these systems is the transfer of energy between
zones of the building. The net energy necessary to keep the water loop temperature
in a proper range can be obtained from gas-fired boilers or other energy production
systems.
The heat output of a WLHPS can supply up to 50% of the thermal energy required
for building heating while compensating for heat losses through the enclosing struc-
ture. Such a design approach is realized due to the possibility of using the power of
heat pumps, which is transferred to the water circuit. An important requirement is
the need to ensure the flow rate of water. Therefore, automatic flow regulators oper-
ating on the principle of dynamic control are used, i.e., a constant flow rate of water
in the system is ensured. WLHPS were first presented in the 1960s. WLHPS have
been paid more and more attention as the energy consumption of air conditioning
has increased since the 1990s and have been widely applied in the United States,
Japan, and other countries [14e18].
A detailed analysis of WLHPS is given in Refs. [14e18]. The results of a feasibility
study for applying WLHPS in European climatic conditions are presented in Ref. [17].
The criterion for partitioning Europe into zones is Heating Degree Days (HDD),
.
.
given in kelvin days (K d). Climatic zones of Europe and HDD index are shown in
Table 3.2 and Fig. 3.27.
The annual specific heat consumption for 32 cities in Europe (HDD
2
2500e3500 K.d) vary from 20 to 60 kWh/(m y) and the energy saving of WLHPS
depends on the value HDD index at different internal loads. As a case study, a typical
office building was considered in cities on the Iberian Peninsula: Spain - Madrid, Bar-
celona and Zaragoza; and Portugal - Porto. The gross total inhabited area of the build-
2
ing was 918 m , and it had internal zones with four orientations as well as an inner
zone; see Fig. 3.28. Calculations show that the thermal capacity varies from zone to
zone, ranging from 93% to 107%.
Two different systems were compared: a WLHPS and a conventional 4-tube fancoil
water heating, ventilation, and air conditioning (HVAC) system. Figure 3.29 shows the
simplified schematic configuration for these systems, while the results of comparing
the efficiency of the two systems are given in Tables 3.3 and 3.4.
The climate zones of the USA are shown in Fig. 3.30.
In Ref. [20], a detailed study was reported of WLHPS in comparison with coal-fired
and electric boilers in 12 cities in China (Harbin, Urumqi, Beijing, Jinan, Lanzhou,
Xi’an, Shanghai, Chengdu, Wuhan, Fuzhou, Kunming, Guangzhou). The study
looked at four common building types, a multi-zone floor plan, and covered a wide
variation in climate conditions. The results showed that WLHPS were not competitive