Heat Pump Capacity Effects on Peak Electricity Consumption and Total Length of Self- and Solar-assisted Shallow Ground Heat Exchanger Networks

Abstract

A new "self-assisted" Ground Source Heat Pump (GSHP) system configuration is proposed to address the relatively high peak electricity demand of undersized GSHP systems equiped with auxiliary electric heater. In this configuration, ground heat exchangers (GHE) have two independent circuits: the first circuit is used to inject the extra heat produced by the heat pump into the ground during off-peak operations, while the second circuit is used to extract heat in the winter and reject heat in the summer for space heating and cooling, respectively. This configuration is compared against a "solar-assisted" configuration and a conventional single U-tube configuration. An analytical model for shallow GHE networks is used to evaluate the effects of the heat pump nominal capacity and the borehole total length on the total electricity consumption and peak electricity demand of the three configurations. Resultsshow that the self-assisted configuration reduces the peak electricity demand by 47%, in a case with a 29% undersized GHE network and a 16% undersized heat pump nominal capacity, while it increases the total energy consumption by 4.1%. Using a solar-assisted configuration for the same sizing parameters reduces the peak electricity demand by only 6.3% and the total energy consumption by 3.8%.

Linear model predictive control for the reduction of auxiliary electric heating in residential self-assisted ground-source heat pump systems

“…This control model is applied to a residential single-family house in the Montreal area equipped with a self-assisted GSHP using weather forecasts and weather data from 2017 and 2018. This paper therefore furthers the study of the self-assisted configuration proposed by Eslami Nejad et al (2017).…”

“…The downside of solar assistance for GSHPs is that they require extensive installations with costly solar collectors. Eslami Nejad et al (2017) therefore proposed a "self-assisted" GSHP configuration, wherein the excess compressor power is injected into the ground to thermally assist the GSHP. Even though the self-assisted configuration invariably causes an increase in total energy consumption, its usage can lower peak power demand caused by auxiliary electric heating, thus reducing peak power demand of GSHPs with undersized boreholes without relying on expensive solar collectors.…”

Technical and economic evaluation of a ground source heat pump with thermal and battery energy storage systems for residential dwellings in Quebec

“…In this regard, ground-sourced heat pump systems (GSHP) offer an attractive solution in terms of energy efficiency and sustainability. But one of the major issues for their development is their high initial cost, which has resulted in a payback period of more than 14 years (Nguyen et al 2016;Lu et al 2017;Eslami Nejad et al 2017). Because of this, in cold climate countries such as Canada, their most expensive components (boreholes and heat pumps) are usually designed undersized and topped up with a less efficient auxiliary heating system.…”

“…By using thermal energy storage (TES), the excess heat produced during off-peak periods by the heat pump is stored in the storage medium and used during peak hours to meet the building's energy demand. Eslami Nejad et al (2017) proposed a self-assisted GSHP system that is linked to a double U-tube borehole with two independent circuits. In this system, the ground plays the role of TES so that the excess heat produced by the heat pump during off-peak hours is injected into the ground through one of the U-tubes inside the borehole.…”

“…However, they reported a 4.5% increase in total electricity consumption. In general, coupling the TES system with the GSHP system reduces the systems' peak power consumption significantly, as high as much as 50%, although the total power consumption increases by up to 8% (Shi et al 2021;Hirmiz et al 2019;Eslami Nejad et al 2017). Lv et al (2016) performed a thermal and economic analysis of a GSHP system integrated with a TES system for a typical building in Tianjin through a TRNSYS simulation.…”