Elsevier

Applied Thermal Engineering

Volume 111, 25 January 2017, Pages 936-949
Applied Thermal Engineering

Research Paper
Techno-economic feasibility evaluation of air to water heat pump retrofit in the Canadian housing stock

https://doi.org/10.1016/j.applthermaleng.2016.09.117Get rights and content

Highlights

  • Techno-economic feasibility of air to water heat pump is assessed for Canadian houses.

  • A state-of-the-art housing stock model is used for techno-economic analysis.

  • AWHP retrofit reduced 36% of end-use energy consumption in the Canadian housing stock.

  • AWHP retrofit decreased 23% of GHG emission of the Canadian housing stock.

  • Aerothermal energy captured by HP can be assumed as renewable energy in most provinces.

Abstract

This study was conducted to assess the techno-economic feasibility of converting the Canadian housing stock (CHS) into net/near zero energy buildings by introducing and integrating high efficient and renewable/alternative energy technologies in new construction and existing houses. Performance assessment of energy retrofit and renewable/alternative energy technologies in existing houses in regional and national scale is necessary to devise feasible strategies and incentive measures. The Canadian Hybrid Residential End-Use Energy and GHG Emissions model (CHREM) that utilizes a bottom-up modeling approach is used to investigate the techno-economic feasibility of air to water heat pump retrofit in the Canadian housing stock. The proposed energy retrofit includes an air to water heat pump, auxiliary boiler, thermal storage tank, hydronic heat delivery and domestic hot water (DHW) heating. Energy savings, GHG emission changes and economic feasibility of the air source heat pump retrofit are considered in this study. Results show that there is a potential to reduce 36% of energy consumption and 23% of GHG emissions of the CHS if all eligible houses undertake the retrofit. Economic analysis indicates that the feasibility of air to water heat pump systems is strongly affected by the current status of primary energy use for electricity generation and space and DHW heating as well as energy prices and economic conditions. Legislation, economic incentives and education for homeowners are necessary to enhance the penetration level of air to water heat pump retrofits in the CHS.

Introduction

Shrinking the energy footprint of residential buildings is a promising option to reduce national greenhouse gas (GHG) emissions. While developing and implementing improved building codes for new construction is necessary, it is not sufficient to achieve this goal. A housing policy with focus on retrofitting existing houses is an essential part of a strategic plan to reduce the GHG emissions associated with the housing stock [1]. While the most feasible and effective retrofit options might be improving building skin, installing high efficiency heating systems and incorporating renewable energy systems [2], adding an air to water heat pump (AWHP) system to a house could also be a suitable option to reduce energy consumption [3]. AWHP system can provide space and domestic hot water (DHW) heating energy requirement from a single source. While the AWHP system is well established in Europe and Japan, it is relatively new to the Canadian market [4]. Thus, an accurate and comprehensive study is needed to investigate the feasibility of integrating AWHP systems into the Canadian housing stock (CHS). Recently, such studies have been conducted for various regions of the world. For example, Kelly and Cockroft [5] developed a numerical model to evaluate the performance of AWHP retrofit into a building in Scotland. The simulation results were validated by laboratory data and the model was integrated into a whole building performance simulation software. The model was well representative of the AWHP operating conditions in the field trial. An equivalent condensing natural gas boiler and an electric heating system were used as alternative heating systems for the building, and annual energy consumption of the three systems were compared. The results showed that GHG emissions of AWHP were lower compared to that of the condensing natural gas boiler and the electric heating system. While the operating cost of the AWHP exceeds that of the gas condensing boiler, incentives available for renewable thermal energy may make up the difference. In another study, Kelly et al. [6] used the AWHP model to estimate the effectiveness of integrated AWHP and thermal storage tank with phase change material (PCM) to restrict the AWHP operation to the off-peak periods. The results showed that through manipulation of the PCM chemistry, heat storage tank volume could be reduced by 50% with a minimum impact on heat supply to the building in the UK climate. Cabrol and Rowley [7] used a numerical model to study the performance of air source heat pump water heating (ASHP-WH) system with hydronic heat delivery in various UK locations. A sensitivity analysis was conducted to evaluate the impact of the building construction materials and off-peak period operation. The GHG emissions and operating cost of ASHP-WH were found to be lower compared to those of an equivalent size gas boiler, and the annual coefficient of performance (COP) of the ASHP-WH was found to be about 3.5 and 4 for cold and mild UK climates, respectively. Johnson [8] found that in the UK context the heat pump GHG emissions due to electricity consumption were higher compared to gaseous fuels and lower compared to heating oil. Using a model for ASHP-WH system model based on measured data from a field trial campaign Madonna and Bazzocchi [9] found that climate has a significant role on the performance of ASHP-WH, and depending on climate, the energy requirement for space heating could be reduced by up to 79% in new buildings in Italy. A study by Hewitt et al. [10] that investigated AWHP retrofit options for existing houses in the UK recommended using variable speed compressor, advanced evaporators and improving heat delivery system to enhance the performance of AWHP in the European maritime climate conditions. Bertsch and Groll [11] designed, simulated, constructed and tested an ASHP water or air heating system with an operating range of −30 °C to 10 °C and return water temperature of 50 °C for northern US climates. The issues related with the low temperature, high lift operation of the heat pump were dealt with through design choices. The cost of the proposed ASHP system was found to be lower compared to an equivalent ground source heat pump. Ibrahim et al. [12] developed a simulation model to study the performance of ASHP-WH system and its potential for energy savings and GHG emissions reductions in Lebanon. The results showed that COP would vary in the range of 2.9–5 for the various climatic conditions of Lebanon. Lund et al. [13] evaluated the role of district heating in the future renewable energy systems of Denmark assuming that Danish energy supply will be entirely from renewable resources by 2060. Assuming a 75% reduction in space heating demand individual heat pump systems were found to be the best alternative to existing fossil fuel systems. The European Parliament and Council also identified the aerothermal, geothermal and hydrothermal energy production of heat pump systems as renewable energy under specific circumstances as published in the Directive 2009/28/EC [14].

To achieve substantial reductions in national energy consumption, massive energy retrofits in building stocks are required. The unique challenges that such massive retrofits require have recently been the focus of researchers. For example, Dall’O’ et al. [15] presented a method to estimate the energy savings due to retrofitting existing houses in a building stock and applied it for five municipalities in the province of Milan, Italy. Amstalden et al. [16] studied the cost-effectiveness of energy retrofit options from house owners’ point of view in the Swiss housing sector, including the effect of various incentives. They concluded that energy price has the most significant impact on the profitability of retrofit options and efficiency retrofits were economically viable with the current energy prices and future energy cost elevations would improve the feasibility of energy retrofits. Tommerup and Svendsen [17] assessed the performance of energy saving measures for existing Danish houses. The study was conducted for two typical buildings and results showed that retrofits were economically viable in 30 years in the presence of sufficient education and training for house owners. Nemry et al. [18] studied the life cycle impact of 72 building types with different construction properties in various geographical locations of European Union countries. The results showed that heating demand was the dominant energy consumption component in the life cycle energy consumption of both existing and new buildings. It was also found that in most buildings at least 20% energy savings were cost effective with infiltration reduction by sealing and additional roof and façade insulation.

In order to focus efforts and resources to reduce residential energy consumption and GHG emissions an accurately designed strategy with specific goals is required. For this purpose, so far, a wide range of retrofit options including envelope modifications such as glazing and window shading upgrades, as well as installation of solar domestic hot water (SDHW) systems, phase change material (PCM) thermal energy storage, internal combustion engine (ICE) and Stirling engine (SE) based cogeneration systems and solar combisystem were studied [19], [20], [21], [22], [23], [24], [25], [26], [27] as part of a national effort in Canada [28]. In this work, the techno-economic feasibility of AWHP system retrofit in the Canadian housing stock is studied.

Section snippets

Methodology

Under the current circumstances where GHG emissions are considered to be as important as energy consumption and costs, the evaluation of the feasibility of an energy retrofit measure for a house has to consider house energy consumption, associated GHG emissions and energy costs before and after the retrofit. To evaluate the feasibility of massive implementation of energy efficient retrofits in a regional or national housing stock, a representative and accurate housing stock model is necessary

Accounting of renewable energy from heat pump

European Parliament and Council in the Directive 2009/28/EC [14] identified the gross final consumption of energy from renewable resources as the summation of (a) gross final electricity consumption, (b) heating and cooling gross final energy use and (c) gross final energy use for transportation from renewable sources. In accordance to part (b) aerothermal, geothermal and hydrothermal energy of heat pump can be assumed as renewable energy in a case that final gross thermal energy production

Economic analysis based on tolerable capital cost

Accurate estimation of AWHP system capital costs, at residential as well as commercial scale, is difficult because installed costs can vary significantly depending on the scope of the plant equipment, geographical area, competitive market conditions, special site requirements, and prevailing labor rates. Therefore the purchase and installation costs of AWHP systems in Canada vary substantially from manufacturer to manufacturer and location to location. Thus, it is not practicable to estimate

Results and discussion

The CHREM estimates of the current energy consumption and GHG emissions of the CHS are given in Table 7. Swan et al. [32] verified the validity of these results by comparing them with other estimates of Canadian residential energy consumption.

Using the criteria given in Section 2.2, eligible houses for the AWHP retrofit in CHREM were identified. As shown in Table 8, about 71% of the houses in CHREM, representing approximately 6.3 million existing houses in the CHS are eligible for the AWHP

Conclusion

Techno-economic impact of air to water heat pump (AWHP) system on the energy consumption and GHG emissions of the Canadian housing stock (CHS) is presented and discussed. The AWHP system delivers aerothermal energy to the water for space and domestic hot water (DHW) heating purposes. The study was conducted using the Canadian Hybrid Residential End-use Energy and GHG emissions (CHREM) model. A high resolution and versatile whole building performance simulation software, ESP-r, was used to model

Acknowledgement

The authors gratefully acknowledge the financial support provided to this project through the NSERC funded Smart Net-Zero Energy Buildings Strategic Research Network and V.I. Ugursal’s NSERC Discovery Grant. Rasoul Asaee is thankful to the Atlantic Computational Excellence Network for the ACENET Research Fellowship.

Computational resources for this study are provided by the Atlantic Computational Excellence Network (ACENET), the regional advanced research computing consortium for universities in

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