The closed greenhouse is an innovative concept in sustainable energy management. In principle, it is designed to maximize the utilization of solar energy through the
seasonal storage. In a fully closed greenhouse, there is not any ventilation window. Therefore, the excess sensible and latent heat must be removed, and can be stored using
seasonal and/or daily
thermal storage technology. This stored excess heat can then be utilized later in order to satisfy the
thermal load of the greenhouse. Thermal energy
storage (TES)
system should be designed based on the heating and cooling load in each specific case. Underground
thermal energy
storage (UTES) is most commonly chosen as
seasonal storage. In addition, a stratified chilled water (SCW)
storage or a phase change material (PCM)
storage could be utilized as short term
storage system in order to cover the daily demands and peak loads. In this paper, a qualitative economical assessment of the concept is presented. Here, a
borehole thermal energy
storage (BTES)
system is considered as the
seasonal storage, with a PCM or a SCW daily
storage system to manage the peak load. A BTES primarily stores low temperature heat such that a heat pump would be needed to supply the heat at a suitable temperature.
A theoretical model has been developed using TRNSYS to carry out the energy analysis. From the economical feasibility assessment, the results show that the concept has the potential of becoming cost effective. The major investment for the closed greenhouse concept could be paid within 7-8 years with the savings in auxiliary fossil fuel considering the seasonal TES systems. However, the payback time may be reduced to 5 years if the base load is chosen as the design load instead of the peak load. In this case, a short-term TES needs to be added in order to cover the hourly peak loads.