Condensation Heat Gains on Unglazed Solar Collectors in Heat Pump Systems

The performance of ground coupled heat pump systems with borehole heat exchangers can be significantly improved by unglazed solar collectors. In this combination, collector operation temperatures below the ambient air level and hence additional condensation heat gains occur. For an investigated and monitored system in Limburg, Germany, the condensation yield was determined to 3.7% or 19 kWh/(a m2). Thereby, condensation shows a significant dependency on the season. During the summer months, only 0.8% of the total collector yield is induced by condensation, while in winter it increases to 13%. The implementation of an established condensation model to the collector model according to EN 12975 is demonstrated. As main result the investigated the heat pump system performance is only marginally improved due to the condensation heat gains.