GHGI is the total greenhouse gas emissions associated with the energy required to operate a building. It is a metric that is used to reduce the operational greenhouse gas emissions of new buildings.
Various forms of GHGI metrics and similar GHG metrics have been used across many industries in the past. This article is focused on the GHGI metric used to define the City of Vancouver’s compliance limits for new buildings. This metric is being adopted by other municipalities in British Columbia (BC).
What does GHGI mean?
GHGI stands for Greenhouse Gas Intensity.
It is a measure of the greenhouse gas emissions associated with the use of all the energy required to operate a building. Operational energy uses include space heating, lighting, air conditioning, heating hot water, and many other end uses. It is quantified on an annual basis, so when thinking about Green House Gas Intensity, one should imagine a building over the course of one full year.
GHGI is quantified on a floor area basis. It is the amount of emissions (in kilograms of carbon dioxide equivalent – CO2e) divided by the floor area of the building (in meters squared). The unit for GHGI is kgCO2e/m2. As mentioned previously, it is on an annual basis. If a 10,000m2 building emits 55,000 kgCO2e and a 1,000m2 building produces 5,500 kgCO2e, both buildings have a GHGI value of 5.5 kgCO2e/m2 per year.
How is GHGI related to TEDI and TEUI?
All three metrics were introduced as performance limits for new buildings. The purpose of these metrics is to reduce the operational energy and the associated greenhouse gas emissions of a building.
TEDI stands for Thermal Energy Demand Intensity. It is a measure of the thermal energy (energy in the form of heat) required by a building for space conditioning and for conditioning of ventilation air. The following article should quickly bring any reader that is not familiar with TEDI up to speed: https://edgesustainability.com/improvements-to-tedi-and-the-associated-impacts/
TEUI stands Total Energy Use Intensity. It is a measure of the total energy required to operate a building. For readers not already familiar with TEUI, the following article has you covered: https://edgesustainability.com/teui-explained-and-tips-to-improve/
The common aim of the three metrics is to reduce greenhouse gas emissions. As detailed in the above articles, TEDI is a subset of TEUI. Reducing TEDI, reduces TEUI. Similarly, TEUI is a subset of GHGI. Therefore, it is fair to say that GHGI is the most important of these three metrics. The overarching intent of both TEDI and TEUI is reducing greenhouse gas emissions, which is precisely the purpose of GHGI.
How is GHGI calculated?
The total energy required to operate a building for a full year must first be determined (this informs the building’s TEUI value). The fuel type for each energy end use must then be chosen. The emissions factor for each fuel type must then be applied to determine the GHGI contribution of each end use.
The emission factor of a fuel is the quantity of greenhouse gas emissions per unit of energy; it is expressed in kgCO2e/kWh. When calculating TEUI, the annual energy attributed to each end use in a building is expressed in kWh. Applying the emission factor, based on the type of fuel consumed, gives the equivalent annual kgCO2e for each end use. Dividing this total annual quantity of greenhouse gas emissions by the floor area of the building gives the desired unit for GHGI of kgCO2e/m2 per year.
How can the GHGI value be improved?
Improving the GHGI value of a building means reducing that value. Any decrease in the greenhouse gas emissions of the building will reduce this value.
As previously outlined, reducing TEDI reduces TEUI which in turn reduces GHGI. Therefore, any improvements to these metrics will reduce GHGI. The previously linked articles contain guidance on ways to reduce both TEDI and TEUI; all these methods are ways to reduce GHGI.
Once a building’s design has been refined to optimize the quantity of energy used by the building, the most straightforward way to reduce GHGI is to fuel switch. Fuel switching means changing the fuel type used by an energy end use in a building. Fuel switching can reduce GHGI if a fuel with a high emission factor is replaced with a fuel with a lower emission factor. In BC, this usually means switching from natural gas to electricity. Using the emissions factors currently defined by the City of Vancouver, natural gas has an emissions factor that is almost 17 times that of electricity. For example, if a building is designed to generate hot water using natural gas boilers, switching the design to electric boilers can greatly reduce the GHGI value of the building.
On-site electricity generation and purchasing renewable electricity or natural gas are other methods that can reduce a building’s GHGI value.
How do emissions factors influence GHGI?
The emissions factors of different fuel types have a direct impact on GHGI. As described previously, an emission factor is applied to each energy end use based on the type of fuel being used. The energy use is multiplied by the emission factor to calculate the greenhouse gas emissions. If the emission factor of a fuel is doubled, the emissions associated with all energy end uses that use that fuel type will be doubled as a result.
The City of Vancouver currently defines the emission factor for electricity as 0.011 kgCO2e/kWh and natural gas as 0.185 kgCO2e/kWh. The emission factor for natural gas is almost 17 times that of electricity.
There have been recent murmurings, at a provincial level, that the emissions factor of the electricity grid will be updated. The potential update would be aimed at better capturing the interconnectivity of the electricity grid in BC. The province generates a large amount of electricity using hydro power which has low operational emissions. This has led to a low emissions factor for electricity; this method of calculation is simplistic and only accounts for electricity generated and consumed in BC. However, the grid is connected to neighbors which use more emission intensive means of generating electricity, such as natural gas generation stations. The updated approach, which would take a wider view by accounting for interconnectivity of the grid, could greatly increase the emissions factor for electricity in BC.
If the emissions factor of electricity is increased, the GHGI for every building will increase. This is because electricity is the largest fuel type, on an energy uses basis, in most new buildings. This update would make it more difficult to achieve low GHGI values in new buildings.
What is the best approach to achieving a low GHGI?
In general, when designing a building to achieve a low GHGI value the process shown in the below graphic is the best approach.
Note that the above graphic is a very general approach; it is a very simplistic. In reality, each building will have different design considerations which the design team should evaluate before determining the optimum way to achieve the desired GHGI value.
Is reducing the GHGI value a positive thing?
Reducing the greenhouse gas emissions of a building can only be seen as a positive in the efforts to combat global warming. GHGI is a metric used to drive down the greenhouse gas emissions of new buildings. It is a suitable metric that is successful in achieving the desired goal.
Reducing GHGI can increase the operational costs of a building. In particular, fuel switching to achieve a lower GHGI will significantly increase energy costs as electricity is almost three times the cost of natural gas per unit of energy.