Optimal Planning of a Micro-combined Cooling, Heating and Power System Using Air-Source Heat Pumps for Residential Buildings

Abstract

This chapter explains a methodology for optimal planning of a micro-combined cooling, heating and power system driven by a solar dish Stirling heat engine. The solar dish concentrator collects the sun radiations and transforms them into thermal energy. The absorber and thermal storage systems are employed to absorb and store the thermal energy collected by a solar dish for continuous energy supplying when the sunlight is insufficient. The solar energy is absorbed and transferred to the working fluid in the hot point of the Stirling engine. The air source heat pump has been proposed to cool and heat the residential buildings in hot and cold weather conditions, respectively. During a hot weather, the air to air heat pump receives heat from the inside air and transfers it into the outside air, and vice versa in a cold climate. The heating energy obtained from air source heat pumps is not generated by a combustion process, rather it is transferred from the inside air to the outside air. Hence, the most promising aspect of the proposed micro-combined cooling, heating and power system is that it can be solar driven and transfer heat from the inside air during summer. Note that the process is reversed in winter times. Due to the increasing rate of carbon dioxide and more attention paid to the greenhouse gas emissions, use of solar energy and air source heat pumps in a micro-trigeneration system, which does not use any fossil fuel such as gasoline or natural gas, not only gives more chances to significant reduction of carbon dioxide, greenhouse gas emissions, and environmental pollution, but also increases the economic saving in fuel consumption. In an air to air heat pump, the electricity energy is only used by indoor/outdoor fans, and a compressor. Hence, the small-scale tri-generation system consumes less electrical energy than the traditional ones. In order to conduct an optimization, the mathematical model and thermodynamic analysis of proposed microsystem have been provided. Several key parameters related to solar dish Stirling heat engine and air to air heat pumps have been selected as the decision variables to minimize the cost of the electricity energy purchased from the main grid.

Appendix

The specifications of the solar powered Stirling engine are considered as follows [25, 28]:

$I = 1000\,{\text{Wm}}^{ - 2}$, $C = 1300$, $\varepsilon = 0.9$, $\eta_{0} = 0.9$, $K_{0} = 2.5\,{\text{WK}}^{ - 1}$, $n = 1$, $C_{v} = 15\,{\text{J}}\,{\text{mol}}^{ - 1} \,{\text{K}}^{ - 1}$, $R = 4.3\,{\text{J}}\,{\text{mol}}^{ - 1} \,{\text{K}}^{ - 1}$, $T_{{H_{1} }} = 1300\,{\text{K}}$, $T_{{L_{1} }} = 290\,{\text{K}}$, $\xi = 2 \times 10^{ - 10}$, $h = 20\,{\text{Wm}}^{ - 2} {\text{K}}^{ - 1}$, $\lambda = 2$, ${1 \mathord{\left/ {\vphantom {1 {M_{1} }}} \right. \kern-0pt} {M_{1} }} + {1 \mathord{\left/ {\vphantom {1 {M_{2} }}} \right. \kern-0pt} {M_{2} }} = 2 \times 10^{ - 5} \,{\text{sK}}^{ - 1}$, $\delta = 5.67 \times 10^{ - 8} \,{\text{Wm}}^{ - 2} {\text{K}}^{ - 4}$, $\varepsilon_{H} = \varepsilon_{L} = \varepsilon_{R} = 0.9$,$\eta_{elec} = 0.95$

The electricity energy price at each hour has been reported in Table 15.3 [28].

Table 15.3 Hourly electricity price

The specification of the AAHP’s refrigeration cycle and the electric chiller’s COP are given as follows [29]:

$P_{1} = 100\,{\text{kPa}}$, $P_{2} = 800\,{\text{kPa}}$, $T_{1} = - 20\,^{\text{o}} {\text{C}}$, $T_{2} = 50\,^{\text{o}} {\text{C}}$, $T_{3} = 30\,^{\text{o}} {\text{C}}$, $T_{4} = - 25\,^{\text{o}} {\text{C}}$, $h_{1} = 387.2\,{\text{kJ}}\,{\text{kg}}^{ - 1}$, $h_{2} = 435.1\,{\text{kJ}}\,{\text{kg}}^{ - 1}$ $h_{3} = h_{4} = 241.8\,{\text{kJ}}\,{\text{kg}}^{ - 1}$, ${\text{Energy}}\;{\text{requirement}}\;{\text{of}}\;{\text{electric}}\;{\text{chiller}}\, = \,0.7\,{\text{kWton}}^{ - 1}$, $COP = 2.46$, ${\text{C}}_{a} = 1.15\,{\text{kJ kg}}^{ - 1} {\text{K}}^{ - 1}$, $m_{in - air} = 0.2\,{\text{kg}}\,{\text{s}}^{ - 1}$, $m_{out - air} = 0.2\,{\text{kg}}\,{\text{s}}^{ - 1}$, $\dot{m} = 0.2\,{\text{kg}}\,{\text{s}}^{ - 1} \quad {\text{for}}\;{\text{CCP}}\;{\text{mode}}$, $T_{C} = 317\,{\text{K}}$, $T_{e} = 290\,{\text{K}}$

In this chapter, a benchmark residential building with 1080 m² area is assumed in Tabriz, Iran to be delivered cool, heat and power by the proposed micro-trigeneration system. The specifications of the benchmark building are reported in Table 15.4.

Table 15.4 The specifications of the test building [28]

Equipment cost of proposed micro-CCHP system’s components has been reported in Table 15.5.

Table 15.5 Equipment cost of proposed tri-generation system’s components