This section will present the experimental method used in the testing of the dehumidifier, regenerator and complete SDCS. In the laboratory testing of the SDCS, an environmental chamber has been employed to (a) achieve a high level of control and provide consistent inlet air conditions to the SDCS throughout all tests, and (b) simulate different climates other than the UK; specifically those that favour the use of liquid desiccant based air conditioning systems i.e. high relative humidity. The environmental chamber can create air conditions from 0 to 40 °C and 10-80 % relative humidity. Unlike the IDCS tests, the whole SDCS has been placed in the environmental chamber itself, thus providing a realistic
Fig. 6.4 Complete SDCS experimental set-up
representation of the operation of the system under a particular climatic condition. Figure 6.4 provides a photograph of the complete SDCS laboratory experimental set-up, including the environmental chamber and hot water cylinder.
First, the temperature and relative humidity of the environmental chamber are set. Depending on the requirements it can take up to 1 h to achieve stable and homogenous air conditions inside. The temperature and relative humidity within the chamber is shown on the chambers display panel, and is cross checked against the four Vaisalia HMP110 humidity and temperature probes on the SDCS and an RS 1365 handheld humidity-temperature meter. Once the desired air conditions are achieved, and depending on the test variable under investigation, the SDCSs operation is set accordingly and run at that condition.
For the regenerator tests, a vented 120 L hot water cylinder with a 3 kW electrical immersion heater is used as the thermal input to the SDCS. This is placed outside of the chamber and piped though the door to the SDCS using a flexible PVC hot water hose. Before the start of a regenerator test the hot water tank heater and circulation pump (H/P) are switched on. A by-pass loop is used to circulate the water around the tank until it reaches the desired temperature for the particular test. A control valve (V4) is then used to provide the desired hot water flow to the SDCS. The tank thermostat is set according to the required flow temperature, and is checked at regular intervals. Additional control of the flow temperature is achieved by turning the heater on and off manually.
The desiccant solution concentration in both the dehumidifier and regenerator tanks are recorded at the start, mid-point and end of each test, and the results recorded. The air velocity is measured at each duct outlet and recorded at the beginning of a test, and the result recorded. Multiplication of the average air velocity by the air duct area provides the volumetric air flow through the cores. The desiccant solution and water volumetric flow are measured at the start of a test, and the flow indictors checked periodically throughout a test. Depending on the test variable being investigated, tests last for around 30-60 min or until steady- state dehumidifier outlet conditions are achieved for extended periods (30 min or more). Data is logged every 10 s in this period. Only steady state-data is used in the performance evaluation. For each variable investigated there are a minimum of three individual tests conducted. The results presented are the average of each of these tests.
Testing of the dehumidifier and regenerator components are carried out separately in Sects. 6.3.1 and 6.3.2 respectively. This approach was taken to simplify the experimental process and to focus on the particular performance of the component. Using the component test results, evaluation of the complete SDCS in Sect. 6.3.3 is possible. The performance evaluation metrics used in the dehumidifier and regenerator tests are the same as those used for the modelling and IDCS evaluation. The equations used to determine these performance metrics may be referred to in Sect. 3.3.3. In the dehumidifier moisture removal rate, change in absolute humidity of air, latent effectiveness and dehumidifier cooling output are evaluated. In the regenerator: moisture addition rate, latent effectiveness, regenerator thermal input and water temperature difference across the plate heat exchanger are evaluated. For the overall SDCS performance, the thermal and electrical COP (COPth) and (COPei) are used, and are previously defined in Eqs. 4.30 and 4.31 respectively. The thermophysical properties of the humid air are determined from in-built functions in EES (see Appendix 2 for reference), and the thermophysical properties of the desiccant solution are determined from linear regression curve fits to published data (James 1998; Melinder 2007), presented in Sect. 3.2 and Appendix 1. Uncertainty analysis is used to provide a measure of the experimental error associated with the calculated values, using the propagation of error formula, provided in Eq. 5.3. The maximum relative uncertainty values for the dehumidifier and regenerator performance studies are presented in their respective experimental results section.
Section 6.2.2 has described the experimental method used to test the SDCS. Next, Sect. 6.3 presents the results and analysis from the testing of the SDCS.