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144 Low-Temperature Energy Systems with Applications of Renewable Energy

Table 4.1 Research references in the field of heat pump drying.

Researchers Country Application
Chou et al. (1998) Singapore Agrarian and marine
products (mushrooms,
fruits, seafood)
Chou et al. (1998), Carrington, Barneveld, New Zealand Plank timber and wood
et al. (1996), Carrington, Bannister, et al.
(1996), Sun, et al. (1996)
Prasertsan et al. (1997), Prasertsan and Thailand Agrarian crops (bananas)
Saen-Saby (1998)
Mason and Blarcom (1993) Australia Nuts
Meyer and Greyvenstein (1992) South Africa Grain
Rossi et al. (1992) Brazil Vegetables (onions)
Nassikas et al. (1992) Greece Paper
Strommen and Kramer (1994) Norway Marine products (fish)
Hawlader et al. (2006, 2006) Singapore Ginger, guava, papaya
Alves-Filho and Ross (2006) Norway and General studies
Ireland
Sieniutycz (2006) Poland General studies
Sakar et al. (2006, 2006) India General studies
Claussen et al. (2007) Norway Potatoes
Sunthonvit et al. (2007) Australia Nectarines
Van Der Pal et al. (2007) New Zealand Wood
Zhang et al. (2007) China Wood

efficiency of the cooling system. Figure 4.11 shows some of the SMER values for the
typical range of temperatures in a HPD as a function of initial temperature of the drying
agent [21,22].
The characteristic feature, according to Fig. 4.11, is that the amount of moisture
removed per unit of energy consumption is sharply reduced with a decrease in the tem-
perature of a drying agent, mainly due to the decrease in the COP of the heat pump.
The theoretical maximum of SMER for convective heat drying is about 1.55 kg of

moisture/kWh (based on the latent heat of moisture evaporation at 100 C). Typical
values of SMER achieved by heat pumps are about 3 kg of moisture/kWh [23]. While
this is about twice as high as the ideal SMER, it is much better than traditional convec-
tion type dryers that have SMER values in the range of 0.5e1 kg of moisture/kWh.
The overall values of the coefficient of moisture removal efficiency for the HPD are
shown in Fig. 4.12 [24]. The heat pump and the dryer can be combined in different