Numerical simulation of a residential house coupled with a dual source heat pump system

. With the information technology revolution and the improving requirement for indoor air environment, energy consumption for air conditioning is increasing in Tunisia. In this research, a heating a residential house using the abundant and universal sources is proposed for a residential house in Tunisia. The effect of the incidence solar radiation in the coupling of a residential house and a heat pump system in all direction of this zone during the winter has been added. The effect of ON-OFF technology in the level of the evaporator during the winter has been studied. We present a mathematical description of the house on TRNSYS, as well as the numerical results of the simulation of coupling of the several components. The incidence solar radiation, the temperature distribution and the energy consumed and delivered, and its impact on air-conditioning load in rooms have been measured using the Tunisian climate. Numerical results have been obtained for 24h in January and 4500h operation in winter. Results show that the system may be satisfactorily used for residential building or greenhouse heating in the Mediterranean and region of Tunisia.


INTRODUCTION
In the literature, there are many reported theoretical and experimental studies, which explain the thermal and exergetic analysis of residential house (or greenhouse) coupled with more component (solar thermosiphon collector, heat pump system, underground air tunnel system …): A real success of solar integrated energy system requires a good solar cooling and heating system, which is in good match with the solar collector integrated on the roof or wall. Badran et al in [1] have illustrated an experimental study for an inverted trickle solar still. Badran and Jubran in [2] have developed two identical flat plate collectors of the conventional fin tube configuration. Daou et al in [3] have developed a solar cooling system with solid desiccant or liquid desiccant cooling reasonable in humid areas, in which dehumidification is considered important, or dehumidification is integrated with water evaporative cooling. Demand side management by controlling refrigerators and its effects on consumers has been studied in [4].The above solar sorption systems have been also incorporated with a normal vapor compression cooling system to ensure the full availability of heating or cooling for buildings, or a backup heating might be used to drive solar sorption cooling system. The problems for the geometry, the thermal performance, the effect of the solar radiation, the control function and the experimental study and the numerical simulation of the heat pump system coupled with a single house using the TRNSYS software have been improved in previous work such as in ( [5][6][7][8][9][10][11][12][13][14][15][16]).
The objective of this work is to model and simulate the coupling of a residential house and a heat pump system. The effects of the control function and the solar radiation in all direction of the house have been studied. Here, we present a mathematical description of the residential house on TRNSYS software, as well as the numerical results of the simulation of the residential house (type 56a on TRNSYS), such The incidence solar radiation, the temperature distribution and the energy consumed and delivered, and its impact on air-conditioning load in rooms have been measured using the Tunisian climate.

MATERIAL AND METHOD
To simulate the combined system with residential house and heat pump, the software TRNSYS has been used. The simulations were performed in TRNSYS 16[38] during 2012. From these results new simulations have been conducted in TRNSYS 16 and a new report with the results will be available in 2013.

1. Description of the residential house on TRNSYS
This model type (56a on TRNSYS) is useful for estimating heating or cooling loads for a residential house. Walls, windows, flat roofs, doors, and floors are included in this component. The houses consist of a ground floor, an upper floor and a loft (Fig. 1). On the ground floor there is a kitchen, a living room and a toilet. On the upper floor, there are three bedrooms with high ceilings and a toilet (Fig. 1). The main parameters of the heat pump are shown in Table 1.

Heat pump system
A detailed simulation study on the performance of CO 2 in reversible residential heat pumps (type 20 on TRNSYS) gave quite promising results.

Controller of the heat pump
The controllers on TRNSYS are designed primarily for implementing temperature level control Fig. 2. Type 2 is most frequently used to control fluid flow through the heat pump loop on the basis of two Input temperatures. However, any system employing differential controllers with hysteresis can use type 2. Temperature level control in TRNSYS relies on control function, γ, which is typically constrained to [γ min ; γ max ]. Two types of temperature level control are commonly used: continuous control and discrete (On/Off) control. In continuous control, γ can take any value from γ min to γ max .

4. Supplementary material Mathematical Description
In order to solve the basic equations modeling the heat transfer through and between all elements in the zone, the problem is reduced to the following matrix equation. Where T s,i represents the inside surface temperature of element i, unless i is equal to the number of surfaces plus one (n+1), in which case it is the zone air temperature. The factor X i includes time varying Inputs that affect T s , i ., Z i , j is a coefficient relating the heat transfer between elements i and j. The objective is to formulate the problem in terms of, making simplifying assumptions that result in a time independent Z i , j matrix. In this manner, the Z i , j matrix is inverted once at the beginning of the simulation and stored for later use. The solution of the set of equations is then reduced to multiplication of the inverted Z i , j matrix and the time varying X i vector.

Exterior wall
The instantaneous heat flux entering or leaving the zone for an exterior wall can be modeled according to the following transfer function relationship.
The coefficients b h , c h , and d h are transfer function coefficients for current and previous values of the sol-air temperature (T sa,i ), equivalent zone temperature (T eq,i ), and heat flux, q i . A value of h equal to zero represents the current time interval, h equal to one is the previous hour and so on. The sol-air temperature, T sa,i , is the temperature of the outdoor air which, in International Letters of Chemistry, Physics and Astronomy Vol. 55 the absence of all radiation exchanges, would give the same heat transfer at the outside surface as actually occurs. For a vertical wall, it is generally expressed as:

Control function
The evolution of the control function of the heat pump during the first day of January indicates a constant value equal to 0 during the first ten hours (Fig. 2). This value is explained by the fact that the heat pump works with the ambient air on the level of the cold source during this interval of time (Fig. 3). It is worth noting that this evolution announces value 1 during the remainder of the day which explains why the pump functions with the water of a liquid source on the level of the cold source.
According to the value of outlet water temperature of the tank, the controller defines the operating condition of the pump. Thus, if the temperature of water reaches its minimal value indicated by the user, controller automatically indicates the value 0 to make sure that the pump works with the ambient air on the level of the cold source (Fig. 3). If the temperature of outlet water temperature of the tank is favorable for the operating condition of the pump, the controller announces value 1 (Fig. 2). Fig. 4 show the Total energy received and delivered by the heat pump and the energy inside the zone for 24h operation in January. The total energy delivered by the heat pump for one day in January increases in an appreciable way until it reaches the value 10.6 (KW), this increase is accompanied with variation of the energy received by the heat pump. Following the fall of the incidence radiation (15 to 18 pm), this energy decreases to be stabilized around 6.5(KW), which is also followed by decreases energy received by the heat pump and the energy inside the zone. Figs. 5-8 show the outlet water temperature and the COP in the level of heat pump and in the level of the system, the temperature inside the zone and the total energy inside the zone for one day in January and 4500 h operation in winter; all results obtained depend on the incidence solar radiation and the ambient temperature in Tunisia. The highest and the lowest values of the outlet temperature of water in heat pump and inside the zone (Figs. 5, 6-8) are obtained to be 60°C and 24°C, and 20°C and 17°C, respectively. The ambient air temperatures varied from 15.6 to 20°C, the average temperatures inside the zone for 4500 h operation in winter are between 17.5 to 24.00°C (Figs. [4][5][6]. The temperatures inside the zone for 24 h operation in January (Fig. 6) marked a maximum value in southwesterly and south east direction (24 °C between 10 and 16 h; respectively 21°C in north east and northwesterly direction) which is explained by the influence of the solar radiation in this directions and this time.

CONCLUSION
The performance analysis and parameters on the residential house coupled with heat pump system has been carried. The simulation results of two components on TRNSYS (type 56a coupled with type 20) have been obtained. The effects of various parameters on heating mode are analyzed. The COP, the COP sys and the outlet temperature of water on the heat pump, the energy, the temperature and the relative humidity inside the house are determined.
The COP for the heat pump and for the system can momentarily be very high in systems with water, when the temperature to the evaporator is elevated.
As systems with residential building coupled with heat pumps are very complex, it is hard to give general results or design rules. If the system is well-designed regarding heat pump capacity and building load and presuming all subsystems are working well, the best use of water during winter (November-April). The optimum periods for this control strategy depend on the size of the heat load and hot water. A careful design of the system is important in order to minimize the use of electricity. Consequently, 1. When the temperature of water increases, the COP, the COPsys, the temperatures and the energy inside the house increase also.
2. Since the temperature of water received from the tank or surface of water is higher than that of the environment, the compression rate of the compressor is rather low, by means of which it needs less energy from external sources.