Requirement Summary
This measure can be claimed if a power generator fueled by Diesel or Natural Gas provides power to the building, and a recovery technology is installed to capture the waste heat from the generator for the cooling cycle. Additionally, the absorption chiller system must achieve a Coefficient of Performance (COP) greater than 0.7 under ARI conditions. The COP is used to establish the efficiency of this measure.
Intention
In many cases, a cooling system will not be included in the original build, possibly increasing the risk that future occupants will deal with insufficient cooling with an amateur installation of inefficient and poorly sized air conditioning units. By providing a mechanical refrigeration system that uses the waste heat generated in other processes such as electricity generation or industrial processes to run an absorption chiller, the energy needed to deliver the required cooling and/or heating can be reduced significantly.
Approach/Methodologies
EDGE uses COP to measure the efficiency of an air conditioning system. The COP of absorption chillers is the total output of cooling energy per waste heat input. As defined in ASHRAE, the COP is “the ratio of the rate of heat removal to the rate of energy input, in consistent units, for a complete refrigerating system or some specific portion of that system under designated operating conditions.” Compared to mechanical chillers, absorption chillers have a low coefficient of performance (COP = chiller load/heat input), but they are powered by waste heat. The formula to calculate COP is explained below. For consistency, the ARI conditions must be used for comparison of COP values.
Where:
Q out = heating energy removal (kW)
W in = electrical energy input (kW)
To claim this measure, the design team must demonstrate that the absorption chiller(s) achieve an efficiency greater than 70% (COP >0.7). For large buildings with centralized systems, more than one chiller may be installed. If these chillers have different COPs, the weighted average COP must be calculated.
In some cases, the air conditioning system (chiller/s) for the cooling system can be centralized, serving a combination of buildings/dwellings within the development. In these cases, the central plant will need to be included within the site boundary of the project, or managed by a company within the control of the site owner. This is to ensure the continuous sustainable management of (and access to) the facility by the site owner.
However, when the chiller for the cooling system is located off-site, then a contract with (or letter from) the management company in charge of the chiller must be provided, stating the efficiency of the system, as part of the documentation for the post-construction stage.
If air conditioning is not specified, any cooling load will be displayed as “virtual energy.”
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
An absorption chiller is a type of air-cooling device that absorbs waste heat instead of electrical energy to provide cooling. An absorption chiller has a low COP. However, it can reduce operating costs because it is powered by waste heat. An absorption chiller is a much more cost-effective alternative to a traditional cooling system due to the use of waste heat as fuel and lower maintenance.
Waste heat is the result (byproduct) of building processes or industrial processes that is not being put to practical use. This waste heat is captured to generate cooling as an emission-free substitute for costly purchased fuels or electricity. It is thus a no-cost fuel source which can improve the overall energy efficiency in a facility.
Absorption chillers are more cost-effective in large-sized buildings which are owned and operated by the same manager.
Relationship to Other Measures
The local climate, heat gains and internal temperatures based on the building design impact the cooling load. A more efficient system will not impact other measures, but several measures will impact the total energy use of the cooling system.
In addition, when an absorption chiller powered by waste heat is selected as an energy efficiency measure, the heating and/or cooling energy is reduced depending on the load of the building. The energy from pumps is slightly increased due to the operation of the system.
Assumptions
The base case efficiency of the air conditioning system is based on ASHRAE 90.1-2007, and is listed in the Key Assumptions for the Base Case in the Design section. The heating fuel selection can be changed by the user.
The improved case COP for the absorption chiller system is 0.7. Although the equipment efficiency is not high, it uses waste heat to power the chiller, thus achieving a higher whole-system efficiency.
Compliance Guidance
To demonstrate compliance, the design team must describe the specified system and 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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