C. G. Carrington

An empirical model for a heat pump dehumidifier drier

Data obtained from laboratory measurements on a dehumidifier drier using R134a in a scroll compressor are analysed to establish empirical sub-models for the principal drier components. A model for the dehumidifier system is set up by coupling the sub-models using energy and mass balances. The performance data obtained using the system model is in good agreement with the measured data obtained with four system configurations under a wide range of operating conditions. The model is used to demonstrate how the performance for the dehumidifier relates to that for the coupled kiln-dehumidifier system. By resizing the heat exchangers it is shown that the energy efficiency of the prototype system can be increased significantly, the dehumidifier specific moisture extraction rate approaching 10 kg kWh -1 at high humidity.

Impact of kiln losses on a dehumidifier drier

The performance of a heat pump dehumidifier kiln has been measured, and the kiln energy balance assessed, during commercial-scale operation. Test data is presented for four drying tests. The results show that the drying performance of the system is impaired by excessive air exchange between the environment and the kiln, and by losses due to heat conduction through the kiln envelope. The results illustrate the importance of the integrity of the kiln structure for both the system drying speed and its energy efficiency.

Dehumidifier batch drying—effect of heat-losses and air-leakage

The performance of a dehumidifier dryer is influenced strongly by the operating temperature and humidity. This paper shows how heat conduction and air leakage losses can cause the temperature of a dehumidifier kiln to collapse in a batch drying process, resulting in increased drying time and energy use. By means of a dynamic simulation model it is shown that heat loss due to an uninsulated floor alone may be sufficient to prevent a kiln reaching its normal operating temperature. It is shown that the effect of heat losses is exacerbated when the dehumidifier capacity is modulated for humidity control. Auxiliary heating can prevent temperature collapse in a poorly insulated kiln. This maintains the drying speed but adds considerably to the energy used. To avoid these difficulties the insulation and air seals of a dehumidifier dryer should be appropriate to the power dissipated by the dehumidifier and fans. An example is presented in which sealing and insulating the kiln yields a reduction of 44 per cent in the drying time, a reduction of 32 per cent in energy use, and an increase of 168 per cent in net operating revenue. Copyright

VALIDATION OF A DYNAMIC MODEL FOR A DEHUMIDIFIER WOOD DRYING KILN

The validation of a dehumidifier wood drying kiln model established previously has been conducted by using the performance data for a commercial scale kiln. The good agreement between the modelled and measured performance results shows that the model can be used for the design and analysis of dehumidifier wood drying kilns.

Performance of a geared dehumidifier

The performance of a laboratory scale dehumidifier has been measured under controlled laboratory conditions, yielding a maximum dehumidifier specific moisture extraction rate (SMER d ) of 7.94 kg kW -1 h -1 at 50°C and 85% relative humidity. Although we are not aware of any published data on dehumidifier systems having higher SMER d , there appears to be further scope for improvement, as the exergetic efficiency of the unit was in the region of only 4-12%.

Performance of a scroll compressor with R134a at medium temperature heat pump conditions

The isentropic and volumetric efficiency of a scroll hermetic compressor is measured using R134a under medium temperature heat pump conditions. The evaporating temperature ranges from 3 to 36°C and the condensing temperature from 34 to 78°C. The efficiency parameters are fitted to functions of the suction and discharge pressures. At the same port pressures, there are only small differences between the isentropic and volumetric efficiency parameters for R134a and those for R22, the latter determined from the manufacturers data. The efficiency parameters for R134a are used to compare the performance of the compressor with R12, R134a and R152a in a medium temperature heat pump cycle. The COP and heating capacity exhibit trends similar to those in previous experimental data for a reciprocating compressor.