The heat pump dehydrator is a high-efficiency drying system that uses a heat pump to remove water from the air in the dryer, generating very little waste heat. This system recirculates and reuses the heated air in the drying chamber, reducing energy consumption by up to 50% compared to conventional drying systems. The heat pump also has the advantage of using only electric power, eliminating the need for fossil fuels and airborne emissions. In addition, the system has low temperatures and humidity control, making it ideal for drying a wide variety of foods.
The use of a heat pump dehydrator is especially useful for drying specialty crops such as herbs, flowers, fruits and vegetables that require low temperature drying to avoid damaging the nutrient content. These crops can be dried in outdoor environments or using high-temperature industrial dryers, which are expensive to operate and produce a large amount of airborne emissions. Heat pump drying can improve the quality of these products by increasing their nutritional value and retaining their flavor, color and aroma.
In order to optimize the performance of a heat pump dryer, the energy efficiency can be measured by MER (specific moisture extraction rate) and the COP (coefficient of performance). The MER measures the amount of moisture that is extracted per kilowatt-hour, while the COP indicates how much work the compressor performs in order to extract the same quantity of moisture.
Heat pumps can be used to improve the quality of fruits and vegetables by preventing microbial contamination, improving their color and vitamin C contents, enhancing volatile compounds, and preserving their essential oils. It can also increase the yield of these foods by increasing the amount of dry matter and decreasing the amount of water. Furthermore, it can reduce the cost of drying and energy costs, allowing more affordable access to these foods in developing countries such as sub-Saharan Africa.
The main objective of any drying process is to produce a high quality dried product with minimum cost and maximum throughput. It is very difficult to consistently optimize these factors in the same drying conditions for a long time, and hence attention has been directed towards exploring energy saving technologies (Keeye 1978; Strommen 1996). Heat pump drying can improve product quality and reduce operating costs by providing recirculation of latent and sensible heat, which are lost in conventional dryers through venting or convection.
Various research works have been carried out on the application of heat pump drying to food products, including vegetables, fruit and spices. Some of these studies include heat pump drying of sapota pulp to produce sapota powder, which was reported to be better than cabinet or tunnel dryers in terms of microbial safety and colour stability. Another study involved heat pump drying of nectarine slices, which demonstrated improved ascorbic acid retention and lactone and terpenoid content compared to conventional cabinet and tunnel dryers.