Building a Net Zero Commercial Building in Alberta was never going to be easy. The size and expertise of the team required to achieve it, and the amount of time sweating the little details cannot be understated. So what role did using Geothermal (or Ground Source) Heat Pumps have in achieving this lofty goal? Could we have achieved Net Zero using a different system? These are the questions we want to explore in this blog post, using lessons and data from the recently constructed Mosaic Centre. Please note that some of the numbers and data were taken from preliminary design work (decisions had to be made early) so some numbers might have changed for the final constructed building.
The process for achieving Net Zero is pretty much the same for all buildings and can be simplified as follows:
Sounds simple enough, but the first three steps are incredibly challenging, have huge cost implications and take an incredible amount of coordination. The important thing to keep in mind during the entire process is that any energy that we don't save in these first three steps is energy we will need to produce using solar PV. Since producing power with solar PV is not only costly, but we are limited with how much roof area we have for solar modules, there is always a limit to the amount of energy that we can actually produce in a given year. This limit becomes our yearly energy ‘budget’, and to reach Net Zero, we can’t exceed it.
To minimize the lighting and plug loads (step 1), the owner and design team must work to reduce the building’s electrical demand to a bare minimum. For the Mosaic Centre, this meant allotting an energy budget to each tenant, taking advantage of natural daylighting, only providing task lighting in certain areas, specifying high efficiency LED lighting (and controlling it to turn off when not needed), and specifying the most efficient appliances and equipment available. Reducing these loads can only go so far, as the occupants will always need a certain amount of lighting and equipment to run their business. The goal isn’t to disrupt the way people work, just to minimize their energy usage as much as practicable.
In step 2, the building envelope was designed to capture as much sun as possible in the winter and prevent overheating the rest of the year. The Mosaic Centre is actually a cooling dominant building, which means that the balance of loads and levels of insulation required are much different than with a Net Zero residential building. This is typical of commercial buildings because of the gains associated with people, lighting, and equipment (even reduced as much as they were), as well as solar gains which are significant in our province. All of these factors were taken into account during the design process.
One thing to note is that the design of the geothermal system was never done in isolation of the first two steps. The building loads have a huge impact on the size and performance of the ground heat exchanger, so we updated our energy model the entire time. In fact, the same energy model was used for the ground heat exchanger sizing, the net zero design, as well as the LEED submission; this was a natural efficiency we suggested to the client to save time and money on energy modelling services.
Once the building loads were reduced and the envelope was tightened up and optimized, we had to choose a mechanical system. Heating and Cooling represent approximately 30% of the building’s energy consumption, so the selection of the mechanical system can make or break our ability to reach Net Zero. Since burning fossil fuels is not an option for a Net Zero building, our only options (with associated efficiencies) were as follows:
Based on the building heating and cooling demands, and the system efficiencies, the amount and cost of solar PV required for each system to achieve Net Zero was as follows:
We can quickly exclude system 1 because of the extremely high cost of PV required—the cost premium for the PV is much higher than the cost savings of the mechanical system. System 2 (the air source heat pump system) was estimated to cost $80,000 less to install than the geothermal system, but we can see that we would require $160,000 more in solar PV modules. Therefore, the geothermal system (which uses 40% less energy than system 2 and 70% less energy than system 1), is actually the most cost effective option, with a net savings of $80,000 over system 2. Furthermore, with the geothermal system, the client can take advantage of the Accelerated Capital Cost Allowance tax credit (see our resources section) to depreciate not just the geothermal ground loop, but also the building heat pumps at 50% per year. Taking advantage of the ACCA Class 43.2 tax credit is estimated to save the client $35,000 within 3 years (at which time the assets will be 81% depreciated). This obviously improves the financial attractiveness even further (a net savings of $115,000) and considering all the other benefits of a geothermal system (no roof space required, lower maintenance costs, longer lifespan), made it a no brainer decision for the client.
It should also be noted that with the first two options, there would not have been enough space on the roof for all of the PV required; meaning Net Zero would not be achieved. Furthermore, with the VRV delivery system chosen by the client, the cold climate air source heat pumps are not actually practical as a completely separate backup heating system would have to be installed, increasing the cost drastically (the air source heat pumps cannot operate below about -13C). To make matters worse for Option 2, cold climate air source heat pumps are still not considered reliable enough to use in our cold winters, making the comparison more of a hypothetical one. To our knowledge there is not one commercial ASHP installation in Alberta, though a few residential installations have been made in the last 2 years (we will post something on this topic soon).
The conclusion we can draw from this exercise is that to reach Net Zero, a geothermal heating and cooling system is the only viable option. Because the geothermal system uses much less energy than any other system, the size of the PV system is drastically reduced, offsetting any cost premium of the geothermal system. Not only is it a longer lasting, more reliable and more efficient system, but after factoring in the cost of solar PV, it is the cheapest option as well. This conclusion will be true for any commercial building attempting to reach Net Zero—quite simply because it is cheaper to install a geothermal system than to pay for more PV with a much less efficient system.
Note: As an exercise for the owner—using the actual installed price of the geothermal system—a payback calculation was performed assuming the building was not achieving Net Zero (PV costs were not taken into account) and could use a natural gas boiler system as an option. Compared to a boiler/air-cooled chiller system, the geothermal system was calculated to have a 5 year payback when taking advantage of the ACCA tax credit. Without the tax credit, the payback would be in approximately 8-10 years. This was obviously a theoretical scenario for this building, but was generated to illustrate the attractive paybacks of geothermal systems even for smaller office buildings in Alberta (larger buildings would have a more attractive payback).
For more information on the Mosaic Centre please visit themosaiccentre.ca or check out this video by Green Energy Futures:
2013 © Revolve Engineering Inc. - ALL Rights Reserved.
