Requirement Summary
If the project includes an air-cooled chiller, the actual COP of the system must be entered in the software (even if the COP is lower than the default). Savings can be achieved if the air conditioning system is an air-cooled chiller and achieves a Coefficient of Performance (COP) greater than the baseline case under ARI conditions.
Intention
In many cases, a cooling system will not be fitted as part of the original build, increasing the risk that future occupants will deal with insufficient cooling later by installing air-conditioning units that may be inefficient and are poorly sized and installed. Chillers on the other hand deliver cooling through chilled water which has much higher heat capacity than air, allowing heat to be transferred more efficiently. By carefully designing the installation of a mechanical refrigeration system using chilled air as a distributing unit, the energy needed to deliver the required cooling can be reduced. Air-cooled chillers are suitable for climates where water supply is scarce or high humidity reduces the efficiency of the cooling towers.
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 the 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)
To claim this measure, the design team must demonstrate that the chiller(s) achieve a COP greater than the base case. 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, for example, in a district cooling system. 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 as part of the documentation for the post-construction stage. The document must include the efficiency of the system.
If air conditioning is not specified, any cooling load will be displayed as “virtual energy.”
Potential Technologies/Strategies
This measure is based on air-cooled chillers with mechanical compression refrigeration systems. Chillers typically cool water, which is then circulated to provide comfort cooling throughout a building or other location. The system has four components: i) Compressor, ii) Condenser, iii) Thermal expansion valve, and iv) Evaporator. The compressor compresses the refrigerant and pumps it through the air conditioning system at a designed flow rate and pressure. The compressor technology is a way to distinguish the type of air-cooled chillers: Reciprocating chillers, rotary screw chillers, or scroll chillers. Selection must be made based on many factors including the size of the system; for example, reciprocating compressors are typically 3–510 refrigeration tons.
Air-cooled chillers cost significantly less per ton than water-cooled systems primarily because they require fewer components to build and operate and require less support equipment and plumbing. Installation of an air-cooled chiller is faster and easier than that of a water-cooled chiller. However, the efficiency of water-cooled chillers is typically higher because of the higher heat capacity of water compared to air.
Some minimum efficiencies specified by ASHRAE 90.1-2016 are listed in Table 33 with the Air-Cooled Chiller system highlighted. Note that the EDGE App does not use the 2016 standard; 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, and whether the system is optimized for full load or part load operation. This table shows full load values.
Table 33. Examples of current minimum COPs for different types of air conditioning systems, with the air-cooled chiller highlighted
| 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) |
Relationship to Other Measures
The local climate, heat gains and the 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.
Assumptions
The base case for the air conditioning system’s efficiency is listed in the Key Assumptions for the Base Case in the Design section.
The default value for the improved case COP for an air-cooled screw chiller system varies by factors such as building size; if the system efficiency is different from the default then the actual performance must be entered. Energy savings will be calculated accordingly.
Compliance Guidance
To demonstrate compliance, the design team must describe the specified system and provide documentation to support the claims.
| Design Stage | Post-Construction |
|
At the design stage, the following must be used to demonstrate compliance:
|
At the post-construction stage, the following must be used to demonstrate compliance:
|
© Copyright 2020 GBCI. All Rights Reserved.
Comments
0 comments
Please sign in to leave a comment.