Requirement Summary
If the project includes a cooling system, the actual COP of a system must be entered into the software (even if the COP is lower than Base Case). Savings can be achieved if the air conditioning system provides a Coefficient of Performance (COP) greater than the Base Case.
Intention
In many cases, a cooling system will not be fitted as part of the original build, which increases the risk that future occupants will deal with any insufficient cooling later by installing air-conditioning units that may be inefficient and are poorly sized and installed. By carefully designing the installation of an efficient cooling system into the project, the energy needed to deliver the required cooling can be reduced in the longer term.
Approach/Methodologies
EDGE uses the Coefficient of Performance (COP) to measure the efficiency of air conditioning systems. The COP is the total output of cooling energy per electricity input. The COP for cooling is defined as the ratio of the rate of heating energy removal to the rate of electrical energy input, in consistent units, for a complete air conditioning system or some specific portion of that system under designated operating conditions. The formula to calculate COP is explained below. For consistency the ARI conditions should be used for comparison of COP values.
Where:
Q out = heating energy removal (kW)
W in = electrical energy input (kW)
In order to claim this measure, the design team must demonstrate that the equipment achieves a COP greater than the base case COP value. For large buildings, more than one system may be installed. If these air conditioning systems have different COPs, the weighted average COP should be calculated.
In some cases, the cooling system could be centralized, serving a combination of buildings/dwellings within the development. The central cooling plant may be within the EDGE project boundary and controlled by the EDGE client, in which case the technical specifications must be submitted. However, when the plant for the cooling system is out of EDGE project boundary or not controlled by the EDGE client, then a contract with, or letter from the management company in charge of the plant has to be provided, stating the efficiency of the system, as part of the documentation for the post-construction stage.
Potential Technologies/Strategies
Simple air-conditioners fitted in windows and through-the wall unitary air-conditioners are the most common type of air-conditioners used in individual residential units. Apartment buildings may use packaged air conditioners located on roof tops with ducted air flow. However, these are the least efficient types of systems. Various air-conditioning systems are available that achieve higher cooling efficiency, including split air conditioners, multi-split air conditioners, VRF systems and chillers.
Split air-conditioners are direct expansion (DX) mechanical refrigeration systems with a single condenser unit outside serving a single fan coil unit (evaporator) inside the building, with refrigerant carried between the two in narrow tubes through the wall. These do not require ducts, and are more efficient than ducted systems. But they can only serve fan coil units located at a limited distance from the external condenser unit.
Multi-split air conditioners are like split systems, except that a single large condenser unit is connected to several fan coil units with individual tubes. The added advantage is the fewer number of outside units. But these systems can only serve spaces that are at similar temperature conditions.
Variable Refrigerant Flow (VRF) systems are a step up from multi-split systems because they can serve zones with different thermal needs, including zones that may be in heating mode while other zones are in cooling mode. VRF systems accomplish this through compressors that can modulate their speed and the refrigerant flow. The refrigerant is distributed through a piping network to multiple indoor fan-coil units, each capable of individual zone temperature control through a common communications network. The system runs only at the rate needed to deliver the temperature change required by each internal unit. The three basic types of VRF systems include: cooling only, VRF heat pump that provides both heating and cooling but not simultaneously, and VRF with heat recovery that provides heating and cooling simultaneously. VRF systems may be a particularly good option for buildings with multiple zones or wide variance in heating/cooling loads across many different internal zones. As these systems provide individual control and are the most versatile of the multi-split systems, they are relevant for residential apartment buildings. Due to the way the internal units are connected to the external unit, a breakdown of one internal unit will not compromise the rest of the system. The speed of the outdoor compressors can change to operate in a range of 6% to 100% capacity. Capacities have typically ranged from 5.3 to 223 kW for outdoor units and from 1.5 to 35 kW for indoor units, but new products are continually being introduced. Multiple outdoor units can be used if an even greater range of capacity is required.
Although VRF systems are widely used in residential buildings, other cooling systems can achieve good performance, but are not as common for these building types. A good example is chillers. Air-cooled chillers are vapor compression mechanical refrigeration systems with heat exchangers (evaporators) in which heat captured by the process is transferred to the refrigerant fluid. This heat transfer causes the refrigerant to evaporate, changing from liquid (a low pressure) to vapor. As a result, the temperature of the process coolant is decreased to the desired outgoing temperature. Water-cooled chillers are like air cooled chillers; the primary difference is that water is used to provide the condenser cooling. In general, this technology is more efficient than air-cooled chillers.
Some minimum efficiencies specified by ASHRAE 90.1-2016 are listed in Table 1, with the Variable Refrigerant Flow (VRF) system highlighted. Note that these are for comparative illustration only; the ASHRAE standard contains several COP values for each system type depending on the details of the equipment such as the capacity and technology.
Table 32. Examples of current minimum COPs for different types of air conditioning systems
| Type of Cooling System (Air Conditioning) | COP |
|---|---|
| Through the wall, air-cooled, packaged and split < 9 kW | 3.51 |
| Air-cooled, split < 19 kW | 3.81 |
| Air-cooled, single package < 19kW DX and heat pumps | 4.10 |
| Water-cooled, split and single package < 19kW | 3.54 |
| PTAC and PTHP, standard size, all capacities In equation, Capacity = 2.1 kW < Capacity < 4.4.kW | 4.10 – (0.300 × Capacity/1000) |
| Variable Refrigerant Flow, air-cooled, cooling mode < 19 kW | 3.81 |
| Variable Refrigerant Flow, water source, cooling mode < 19kW | 3.52 |
| Variable Refrigerant Flow, groundwater source, cooling mode < 40kW | 4.75 |
| Variable Refrigerant Flow, ground source, cooling mode < 40kW | 3.93 |
| Air Cooled Chiller < 528 kW | 2.985 at Full Load (FL) 4.048 at Part Load (IPLV) |
| Air Cooled Chiller > 528 kW | 2.985 at Full Load (FL) 4.137 at Part Load (IPLV) |
| Water Cooled Chiller, positive displacement <264 kW (Positive displacement = reciprocating, screw and scroll compressors) | 4.694 at Full Load 5.867 at Part Load (IPLV) |
| Water Cooled Chiller, centrifugal < 528 kW | 5.771 at Full Load 6.401 at Part Load (IPLV) |
Note: If a cooling system other than a chiller is installed in a residential building and achieves the desired COP, then this information can be entered manually into the EDGE software, and evidence provided for certification purposes.
Relationship to Other Measures
Passive measures such as improved walls and windows will reduce the energy use from air-conditioning.
Assumptions
The base case value for the efficiency of the air conditioning system will vary by building type and by location. It is listed in the Key Assumptions for the Base Case in the Design section. The default value for the improved case COP for the efficient cooling system also varies by system type; the actual performance of the system must be entered in all cases.
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 |
|
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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