2016 ASHRAE Annual Conference

This paper summarizes a case study of an innovative ground source heat pump (GSHP) system that uses flooded mines as a heat source and heat sink. This GSHP system provides space conditioning to a 56,000 sq ft (5,203 m2) newly constructed research facility, in conjunction with an on-campus existing steam heating system and an air-cooled chiller as supplementary systems. Heat transfer performance and overall efficiency of the GSHP system were analysed using the available measured data from January through July 2014. The performance analysis identified some issues with using mine water for cooling and the integration of the GSHP system with the existing steam heating system. Recommendations were made for the control and operation of the GSHP system for its improved performance. These recommended strategies, in conjunction with the available measured data, were used to predict the annual energy performance of the system. Finally, the energy and cost savings and CO2 emission reduction potential of the GSHP system were estimated by comparing with a baseline scenario. This case study provides insights into the performance of and potential issues with the mine-water source heat pump system, which is relatively less explored compared to other GSHP system design and configurations.

This article attempts to address the issue of making the right choice between a Direct Expansion Ground-Source Heat Pump (DX-GSHP), an Air-Source Heat Pump (ASHP) and a hybrid of the two in a given heating need context. Detailed screening models previously developed for ASHPs and DX-GHSPs are first used to compare the seasonal performance of these two options for a residential building in the cold climate city of Montreal. Then, the performance of a so-called “Hybrid Ground Source Heat Pump (HGSHP)”, integrated air source and ground source system is also investigated. Furthermore, different parameters including borehole total length and heat pump capacity are varied in order to determine the appropriate design in terms of borehole size and heat pump capacity. The results show that by adequate sizing, energy consumption of the DX-GSHP system can be reduced by 50% but performance improvement using HGSHP system is marginal. Such results highlight the importance of further investigations in the area of DX-GSHPs, in order to reduce the borehole installation cost and increase its performance.

Most commercial ground source heat pump systems (GSHP) in the United States are in a distributed configuration. These systems circulate pure water or an anti-freeze solution through multiple heat pump units via a central pumping system, which usually uses variable speed pump(s). Variable speed pumps have potential to significantly reduce pumping energy use, however, the energy savings in reality could be far away from its potential due to improper pumping system design and controls. In this paper, a simplified hydronic pumping system was simulated with the dynamic Modelica models to evaluate three different pumping control strategies. This includes two conventional control strategies, which are to maintain a constant differential pressure across either the supply and return mains, or at the most hydraulically remote heat pump; and an innovative control strategy, which adjusts system flow rate based on the demand of each heat pump. The simulation results indicate that a significant overflow occurs at part load conditions when the variable speed pump is controlled to main a constant differential pressure across the supply and return mains of the piping system. On the other hand, an underflow occurs at part load conditions when the variable speed pump is controlled to maintain a constant differential pressure across the furthest heat pump. The flow-demand-based control can provide needed flow rate to each heat pump at any given time, and with less pumping energy use than the two conventional controls. Finally, a typical distributed GSHP system is studied to evaluate the energy saving potential of applying the flow-demand-based pumping control strategy. This case study shows that the annual pumping energy consumption can be reduced by 66% using the flow-demand-based control compared with that using the conventional pressure-based control.