E27: Recover of Waste Heat from Generator for Space Heating – Above Green

Requirement Summary

This measure can be claimed if an on-site power generator fueled by Diesel or Natural Gas provides power to the building, and a recovery technology is installed to capture the waste heat for space heating.

Intention

Recovering waste heat from power generators helps buildings to significantly reduce fossil fuel consumption, lower operating costs, and limit pollutant emissions by providing useful heat for space heating. Buildings that use fossil fuel energy for heating and that have a power generator as the main electricity source have the potential to benefit from the application of heat recovery systems.

Approach/Methodologies

If this measure is selected, the assumptions in the Key Assumptions on the Design tab must be verified. The user must select the appropriate fuel under ‘Fuel Used for Electric Generator,’ and input the appropriate value for ‘% of Electricity Generation Using [Fuel].’

Potential Technologies/Strategies

In the context of buildings, heat recovery collects and reuses the heat arising from a process that would otherwise be lost. Sometimes, the loss of this heat is intentional, such as in air conditioning, where the purpose is to remove heat from a space. But in the case of an electric generator, it typically has low efficiency and a large portion of the energy input is lost via the exhaust gases and in cooling the equipment jacket. The following image shows the different sources of waste heat and the uses of the recovered waste heat:

Figure 14. Typical Sources of Waste Heat and Recovery Options

This waste heat can be turned into useful space heat with a recovery technology such as one of those indicated in the table below:

Table 40: Recovery technology options

Recovery Technology	Description
Thermal Energy Storage (TES)	Buffer tank where waste heat from different sources is stored and realized later to reduce the heating load during night time.
Seasonal Thermal Energy Storage (STES)	This technology is similar to TES but the heat is kept for longer periods of time, even months. Usually, the heat is stored in a bigger area where a cluster of heat exchanger equipped boreholes is surrounded by bedrock.
Pre-heating	Simply put, waste heat can help to preheat incoming water, air and objects before they are heated to the desired temperature. This can happen in a heat exchanger, where the waste heat is mixed with the incoming air/water to increase its temperature before it enters into a boiler or heater.
Cogeneration or Combined Heat and Power (CHP) system	This is a system that reduces the waste heat used in the generation of power; however, some limitations arise from the engineering cost/efficiency of using small temperature differences on the power generation.
Recuperator	This is a type of heat exchanger with simultaneous flow of hot and cold fluids along physically separated flow paths, transferring heat between the streams.
Heat Pipe Exchanger	This type pf heat exchanger has vacuum-sealed tubes filled with a working fluid (heat pipes) that are used to absorb heat from a warmer surface and transfer it to a cooler surface. The working fluid inside a heat pipe evaporates at the warmer surface and then travels to the colder surface where it transfers that latent heat and turns back into a liquid phase.

Relationship to Other Measures

EDGE calculates the heating load by taking into account the local climate, heat losses and internal temperatures based on the building design. If a heating system is not specified, any heating load will be displayed as “virtual energy.”

When waste heat is recovered from the generator, heating energy consumption of utility fuel is decreased. However, the energy from pumps may increase slightly due to the operation of the waste heat recovery system.

Assumptions

The default base case for the fuel of the electric generator is Diesel, as listed in the Key Assumptions for the Base Case in the Design section. The fuel can be changed to Natural Gas if that is the main fuel powering the generator. In the same section, the default assumption for the percentage of annual electricity provided by the generator is 5%. The user must input the appropriate value for ‘% of Electricity Generation Using [Fuel]’ to update this default. Justification and documentation must be provided for these key assumptions.

Compliance Guidance

To demonstrate compliance, the design team must provide the following documentation to support their claims.

Design Stage

Post-Construction Stage

At the design stage, the following must be used to demonstrate compliance:

Manufacturer’s data sheets for the electric generator specifying hours of operation and coverage of the demand; and
Manufacturer’s data sheets for the recovery technology used; and
Mechanical and electrical layout drawings showing the location of the generator, the recovery technology and the output for the space heating system; and
Calculation to demonstrate that waste heat covers the percent of the demand for space heating as calculated in the EDGE software.

At the post-construction stage, the following must be used to demonstrate compliance:

As-built mechanical and electrical drawings with the location of the generator, the recovery technology and the output for the space heating system; and
Delivery notes showing that the specified electric generator and the recovery technology have been delivered to the site; and
Manufacturer’s data sheets for electric generator; or
Photographs of installed external and internal equipment related to the system.