Requirement Summary
If the project includes a Variable Refrigerant Flow (VRF) system, the actual COP of the system should be entered in the software (even if the COP is lower than baseline). Savings can be achieved if the air conditioning system achieves a Coefficient of Performance (COP) greater than baseline under ARI conditions. Note that the same measure applies to a Variable Refrigerant Volume (VRV) cooling system, which is a patented name for a type of VRF system.
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 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 the COP is explained below. For consistency, 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 system achieves a COP greater than the base case of 3.5. For large buildings with centralized systems, more than one system may be installed. If these systems have different COPs, the weighted average COP must be calculated.
In some cases, the air conditioning system for the cooling system may 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 plant for the cooling system is located off-site, then a contract with, or letter from the management company in charge of the cooling plant must be provided as part of the documentation for the post-construction stage. The document must include the efficiency of the system.
EDGE calculates the cooling load by accounting for the local climate, heat gains and the internal temperatures based on the building design. If air conditioning is not specified, any cooling load will be displayed as “virtual energy.”
Potential Technologies/Strategies
A Variable Refrigerant Flow (VRF) system uses refrigerant as the medium for heat transfer. These systems have one condensing unit with multiple indoor units, each of which can be individually controlled. The system runs by modulating the amount of refrigerant that is sent to each evaporator, running only at the rate needed to deliver the cooling required by each internal unit. VRF systems may be the best for buildings with multiple zones or a wide variance in cooling or heating loads across many different internal zones requiring individual control such as offices, retail buildings, education, healthcare buildings, or hotels and resorts. The outdoor units can be fitted to as many as 48 internal units. Due to the way in which the internal units are connected to the external unit, a breakdown of one internal unit will not compromise the rest of the system. The outdoor units can vary the speed of the compressors and operate in a range of 6% to 100% capacity. Multiple outdoor units can be used if an even greater range of capacity is required.
Some minimum efficiencies specified by ASHRAE 90.1-2016 are listed in Table 34, 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 34: Examples of current minimum COPs for different types of air conditioning systems, with VRF 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 x 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. A VRF system will have a smaller impact on savings if the building walls and windows have been optimized. To realize savings from a VRF system, the spaces must be zoned separately with their own individual thermostats.
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 default improved case COP for the VRF cooling system varies depending on factors such as the building area; if the designed system efficiency is different than 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 Stage |
|
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.