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Okanagan Case Study Reviews the Energy Efficiency Impact of
Domestic Electric Water Heaters within the Wilden Living Lab.

By Piyaruwan Perera and Anber Rana, PhD Students @UBC Okanagan

 For most of us a hot shower or warm bath is what keeps us comfortable through the winter months. But since showering and bathing also accounts for over 40% of our hot water usage, it is worth looking at how to safe energy and cost while enjoying a continuous hot water supply in your house. 

Domestic water heating (DWH) in residential buildings in Canada accounts for nearly 20% of energy consumption which accounts for a substantial amount of domestic greenhouse gas (GHG) emissions (Amirirad, Kumar, & Fung, 2018). According to Natural Resources Canada (NRCan), DWH contributes about 6 Million-tonnes of CO2 equivalent each year toward national GHG inventory. 

 

Figure 1 shows that the highest water consumption in a household are showers, faucets and laundry machines.

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Options of Domestic Water Heaters:

Storage water heaters (SWHs) are the most common types of heaters used for homes in Canada. SWHs store heated water in an insulated tank and make it available for use with minimum heat loss. A thermostat is used to set temperature for heated water through the use of an electric element or burner (NRCan, 2012). Some other types of DWH are boilers, heat pump water heaters, combination systems, solar water heaters and tank-less (on demand) water heaters (Johnson & Beausoleil-Morrison, 2016). 

Water Heaters in the Wilden Living Lab Homes:

In the Wilden Living Lab, we have used electric storage water heaters (SWHs) using grid electricity provided through FortisBC. We have used air source heat pump mounted an insulated tank system (hybrid system) in the home of tomorrow (HOM) whereas a conventional electric storage water heater is being installed in the home of today (HOD). The hybrid system takes heat from the surrounding air and utilize that heat to increase the water temperature, which lead to greater efficiency. The Energy Factor (EF) metric for the hybrid system is about 1.6 times higher than the conventional water heater, which means that the amount of hot water produced per unit of fuel used is 1.6 times higher. 

The water consumption of both houses were obtained from the latest utility bills, and average daily water consumption was calculated. Moreover, the average daily energy consumption for water heating and water temperature data were measured using sensor-based monitoring data. As per the observations, the volume of water used in HOM is higher than the HOD. Additionally, based on the actual data, the hot water temperature set point of HOD is higher than the temperature set point of the DWH in the HOM. The average hot water usage of both houses was calculated using Equation 1. 

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Where, EF – Energy factor, M – Mass water drawn (kg), Cp – Specific heat of water (kWh/kg.°C), T tank – Water heater thermostat set-point (°C), Tinlet – Inlet water temperature (°C), and Qdm – Water heater daily energy consumption (kwh). The Cp has been obtained as 4.187 kJ/kg.°C (at 15°C) from the literature. 

 

Based on the calculations, 

  • Domestic hot water consumption of HOD is 0.286 cubic meter/day 
  • Domestic hot water consumption of HOM is 0.381 cubic meter/day 

 

Considering above temperature set-points and hot water usage (human behavioral factors), the estimated annual energy consumption for the hot water usage would be 1881 kWh/year for the HOM and 3138 kWh/year for the HOD. However, the human behavioural (domestic hot water use behaviour) factors have been nullified using fixed parameters for hot-water thermostat set-point (60°C) and the domestic hot water usage (0.286 cubic meter/day) using the energy simulation model developed from HOT2000. 

The results based on the energy model are shown in Table 1. The initial investment cost of the hybrid system (HOM) is 1,200 CAD more than a conventional hot water system. To reduce the upfront costs of the aforementioned high efficient domestic water heating systems, the utility providers in Kelowna are currently promoting heat pump water heaters through rebates of up to CAD 1,000 (“Rebates & offers,” 2018). Although the upfront cost of the upgraded system is significantly higher, the operational cost reduction of 298 CAD is also significant compared to the other savings which resulted in a desirable pay-back period of 4 years. Since the lifespan of an electric domestic water heater is approximately 12-15 years, the use of an 80 gallons hybrid electric water heater appears to be the best option among the two water heater types. 

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Domestic hot water savings may reduce operational energy costs and GHG emissions generated by the household. The findings of this study indicate that upgrading from a conventional domestic water heater to an air source heat pump mounted and insulated tank system (hybrid system) with a higher Energy Factor is more economical and environmentally friendly. 

Selecting appropriate DWH system for your home:

According to the Water Heater Guide (NRCan, 2012) , an appropriate water heater for a home can be selected by the four steps shown in Figure 2. 

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Tips to save energy for DWH:

By reducing the amount of water used and energy consumed, the energy used to maintain the DWH is reduced. Daily hot water use can vary with the number, ages as well as the lifestyle of the occupants in a home. Some of the most common strategies that can help reduce energy consumed in DWH are: 

  1. Use of low-flow shower heads and faucets 
  2. Use of energy-star rated appliances such as a dishwasher, washing machines etc. 
  3. Change the water consumption behaviours of the occupants toward low-hot water consumption 
  4. Choose the best domestic hot water system based on the estimated quantity of daily water use 
  5. Maintain a moderate tank temperature (As per BC Housing’s Design Guidelines & Construction Standards 2014, Hot water temperature must not exceed 49°C (120°F) at points of use by tenants. Hot water storage shall not be below 60°C (140°F) to control the propagation of Legionella bacteria.) 
  6. Insulate water pipes 
  7. Solar thermal domestic hot water systems can be a better alternative to reducing overall energy consumption and GHG emissions of the household. However, the cost associated with these systems needs to be evaluated with the potential savings. (A Kamloops-based study done by NRCan shows that 43% of energy can be saved from the annual domestic hot water energy consumption using a solar water heater with a freeze-protected system) 

 

Stay posted for more real-life data results in the future. In our next blog post we’ll talk about the carbon footprints of different energy uses for the Wilden Living Lab.

References

Join the discussion 11 Comments

  • David says:

    Since 2012 the BC Building has required that thermostats for devices that heat water with electricity and store water must be set to 60C to prevent the growth of pathogenic bacteria including Legionella. In promoting moderate temperatures of 55C you are counseling people to break the law.

  • wildenlivinglab says:

    Thank you very much for the valuable input. The article has now been revised accordingly to avoid confusion.

  • Peter Pollhammer says:

    did you consider hot water on demand? gas or electric.

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