Requirement Summary
This measure can be claimed if a heat recovery device is installed to capture and reuse the heat from the hot water drain pipes with at least 30% efficiency. This does not include heat recovery from laundry waste water, which is a separate measure.
Intention
Recovering heat from the grey water (drain water from showers, kitchens, spa area, etc.) helps to reduce fossil fuel consumption of buildings, lower operating costs, and pollutant emissions by preheating the water for bathrooms, laundry and kitchens as part of the hot water system. Buildings that use energy for hot water have the potential to benefit from the application of heat recovery systems.
Approach/Methodologies
Buildings can benefit from technology to recover heat from grey water, as it can save energy and help decrease the design capacity of water heaters. In order to qualify, the design team must demonstrate that the Hot water system has a ‘heat recovery’ device. EDGE uses an efficiency of 30% for the improved case. The efficiency must be verified using manufacturer specifications.
Potential Technologies/Strategies
In the context of buildings, heat recovery aims to collect and reuse the heat arising from processes that would otherwise be lost. In this measure, heat energy is transferred from the hot waste water from showers, bath tubs, sinks, and dishwashers, etc. to the incoming cold-water pipes directly to water fixtures or to preheat the water being supplied to the hot water heater. Various commercial solutions are available for grey water heat recovery, ranging from non-storage systems (shower-only recovery) to centralized heat recovery, which connects more equipment and augments the possibilities for use of the recovered energy. The following table shows some of the solutions:
Table 42: Grey Water Heat Recovery Solutions
| Types | Description |
| Spiral Design (non-storage) |
Hot water runs through a series of narrow spirals in which it is forced to spin alongside the walls of the heat recovery pipe. The cold water then comes as a counter flow in a spiral pipe swirled around the outside. This design requires small gaps (2cm) to avoid plugging. It is commonly used in residential and small hotels or hospitals. Instead of a spiral system, tubular or rectangular heat exchanger systems can also be used. |
| Accumulation Tank (centralized) | Grey water from different sources is accumulated in a tank, which has an electrical coil (close loop) that transfers the heat to the cold water passing through the grey-water heat recovery unit outside the tank. |
| Parallel Heat Exchange (centralizer) | This is ideal for larger buildings such as hospitals, as it collects the grey water in one pipe that passes through the heat exchanger. It is similar to spiral design but used centrally rather than in each unit. |
Relationship to Other Measures
The hot water demand that the boiler is sized to supply is affected by the rate of hot water use. Hot water use should be minimized first by selecting low-flow taps in washbasins and low-flow shower heads.
This measure reduces both ‘Water Heating’ and ‘Other’ due to pumping water in the system.
Assumptions
The base case assumes no heat recovery from grey water, while the improved case assumes that all the hot water discharge except laundry passes through a heat recovery system with 30% efficiency.
Compliance Guidance
To demonstrate compliance, the design team must provide documentation to support the claims.
| Design Stage | Post-Construction Stage |
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At the design stage, the following must be used to demonstrate compliance:
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At the post-construction stage, the following must be used to demonstrate compliance:
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