Research

Control of Single-room Ventilation with Regenerative Heat Recovery for Indoor Climate and Energy Performance

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Abstract

The Danish government will seek energy-efficiency improvements to meet their targeted aims. Single-room ventilation with heat recovery allows simple installation through the façade and may be broadly deployed in apartments. Danish building regulations require greater than 80% heat recovery in new constructions and will soon require 85%. The development of single-room ventilation units may aim for these requirements as a result. The exhaust temperatures in highly efficient heat exchangers may approach outdoor levels. The cold exhaust cannot contain ample moisture, so vapour will condense on the heat exchanger. Available literature suggests that uncoated rotary heat exchangers transfer this condensate to the supply air, so the drying capacity of the ventilation system may be severely limited. This could raise indoor relative humidities to unsafe levels, which could promote the growth of dust-mites and mould. Controls may increase drying capacity by increasing ventilation airflow, but this may not be sufficient to limit moisture-related risks. This research investigated the added demand-control measure of reducing variable heat recovery to increase drying capacity when using an uncoated rotary heat exchanger in single-room ventilation. Simulations demonstrated that increased airflow sufficiently lowered the relative humidity in living rooms and bedrooms during most hours of the year. Decreased heat recovery was only necessary for a limited number of hours to maintain safe indoor relative humidities in these rooms, and the overall average reduction in heat recovery was less than 3%. The combined measures only succeeded in living rooms and bedrooms, and the results confirmed that rotary heat exchangers should not be used in kitchens or bathrooms, where moisture risks may be unavoidable.