The solar assisted heat pump system is based on a vapor compression refrigeration cycle, as shown in Figure 1. Refrigerant R134a is used as working fluid, due to the environmental and thermodynamic performance considerations. The main system components are:

• evaporators,
  
• compressor,
  
• water tank,
  
• drying chamber and
  
• expansion valves.

The two evaporators are connected in parallel to improve the performance of the system. One of the evaporators acts as an evaporator-collector, collecting solar energy and vaporizing the refrigerant flowing through it. The second evaporator performs as an air-conditioner to cool room air. The water-cooled condenser, which performs as a water heater, is connected in series to an air-cooled condenser which acts as a clothes dryer. This ensures complete condensation of refrigerant vapor and, thereby, increases the system's efficiency.

Fig 1 Schematic diagram of three-in-one solar heat-pump system

The superheated refrigerant vapor leaving the compressor enters the water-cooled condenser and performs water heating. The refrigerant, a mixture of vapor and liquid, leaves the water-cooled condenser and enters into an air-cooled condenser to ensure complete condensation of the refrigerant vapor. The hot air obtained from this condenser is used for drying clothes.

Once complete condensation of the refrigerant has taken place, the refrigerant path splits into two: one goes to evaporator-collector and the other goes to air-conditioned space, to absorb solar energy and thermal energy inside the room, respectively. Superheated refrigerant vapor from the two evaporators mix together and enters into the compressor. Thermostatic type expansion valves are used to regulate the refrigerant mass flow rate.

The system provides the following three applications:

• Water heating: In households, one of largest energy expenses relates to water heating.
• Drying: It is one of the most time consuming and energy-intensive processes for industrial or domestic applications.
• Air-conditioning. Solar energy and air conditioning is a natural and perfect match. The time that air conditioning is most wanted and needed corresponds to the sunniest time.

Kindly contact ilotech@nus.edu.sg for any enquiries

Solar energy is the cleanest and most inexhaustible of all known energy sources. The principle of this solar energy system is to collect solar radiant energy and convert it into useful thermal energy. The low temperature thermal requirement of the heat pump makes the system an excellent match for thermal applications for both domestic and industrial use; such as water heating, solar drying, space cooling, space heating and cooling.

Approximately, half of primary energy resources are consumed in water heating, air conditioning and laundry drying in urban households. Furthermore, in densely populated urban areas, drying clothes is considered a problematic household chore as it is a very time consuming operation (natural drying takes about six hours). This integrated solar thermal system offers considerable potential for energy savings due to improved energy efficiency.

This system can serve three functions simultaneously (full-load) or independently (partial load).

1. Air-conditioning:

Figure. 2 shows the change in room and refrigerant inlet and outlet temperature with time. As seen from the figure, the room temperature stabilizes with time.

Figure 2. Variation of temperature of air-conditioned room with time

2. Water Heating:

As shown in Figure 3, the temperature of the 400 liters of water in the tank increased in a steady manner and reached about 60 oC in nearly two hours.

Figure 3: Variation of water temperature with time

3. Drying:

Figure 4 shows the comparison of experimental moisture content of clothes with time at different drying temperature. It is clear from this figure that the drying rate is increased with increasing drying air temperature.

Figure 4: Comparison of experimental moisture content of clothes
with time at different drying temperature and same air flow rate.

The three applications of the system can be served simultaneously or independently. The presence of evaporator-collector enables the system to operate round the clock. Additionally, the parallel arrangement of the evaporator and evaporator-collector provides better system performance. A large fraction of the energy requirements is met by a combination of energy collected from sun, ambient and the energy recovered from a vapor compression heat-pump system, which also serves as an air-conditioner. The system shows good potential for implementation in commercial and residential applications and provides a new dimension in the process of replacement of conventional energy with renewable energy sources.