How to audit a building to achieve net zero
Building energy audits are not new, however there are several ways to design new buildings and to change existing buildings to meet net zero
- Understand ASHRAE Procedures for Commercial Building Energy Audits and ASHRAE Standard 211-2018, Standard for Commercial Building Energy Audits.
- Compare what is required in a net zero audit versus an ASHRAE audit.
- Introduce a new kind of audit with guiding principles that lead to zero-carbon retrofit pathways.
Net zero building insights
- Buildings trying to achieve net zero can learn a lot from energy audits.
- A revision to building energy audits starts with and prioritizes the investigation of renewable, low- or zero-carbon energy sources.
More than 640 climate emergencies have been declared as of November 2022 by municipalities in Canada, and similar declarations for many other cities around the globe have also been made. A municipality with one of the largest city populations in North America has declared it will be net zero by 2040. What is the plan to achieve these necessary — as detailed by climate scientists and the Intergovernmental Panel on Climate Change (IPCC) — but aggressive emission reductions?
A significant sector for emissions reductions is the building sector. Municipalities have been releasing request for proposals for net zero retrofits for their corporate buildings that call for what are essentially cost studies to get to net zero by 2050 or earlier and these requests include ASHRAE audits. A summary of ASHRAE audit steps:
- Assemble audit and implementation team.
- Collect historical energy data and preliminary analysis.
- Site visit.
- Energy efficiency measure types.
- Economic analysis.
- Developing an audit report.
- Implementing measures.
While the ASHRAE Procedures for Commercial Building Energy Audits was first published in 2004 and second edition in 2011 as a “go to” reference, followed by similar guidance from ASHRAE Standard 211, it was not meant for a net zero emissions target. This is apparent from the growing and additional RFP requirements. ASHRAE audits are still relevant and based on experience with net zero studies, and they have a role to play in a net zero pursuit.
While the scope of an ASHRAE audit for a deep energy retrofit compared to an audit where the goal is net zero are similar, there are significant differences in what should be seen and investigated by auditors.
The goal of emissions reduction may be implicit in the procedures or ASHRAE Standard 211 or could be an indirect result of energy reduction, but there isn’t explicit guidance to an auditor when the mandate is net zero emissions. Auditors are being asked to improvise from the existing guidance or make attempts to integrate a plethora of additional requirements alongside an ASHRAE audit.
Shouldn’t a more methodical approach be proposed? What are some guiding principles in this new audit, which has leapfrogged auditors into the next normal of net zero?
Before continuing the conversation on these guiding principles, a definition of a zero-carbon building as well as local energy markets can provide context.
Zero carbon buildings and local energy markets
Architecture 2030 has a definition for a Zero Net Carbon Building and the Canada Green Building Council’s Zero Carbon Building – Design Standard also has the same definition:
“A highly energy-efficient building that produces onsite or procures carbon-free renewable energy or high-quality carbon offsets in an amount sufficient to offset the annual carbon emissions associated with building materials and operations.”
Regarding materials for new buildings and for this discussion on existing building audits, the focus will be on operational emissions.
Building emissions in the Canadian — and specifically Ontario — context come from burning natural gas for space and water heating and peak electricity generation. Emissions from power generation are not significant when compared to emissions from heating. In Ontario, buildings are fortunate that generation is mostly from low carbon emitting sources such as nuclear and hydro power.
Thus, the challenge essentially reduces to eliminating natural gas use; the pathway to building decarbonization in Ontario (as with many jurisdictions with cleaner electricity grids) is electrification. The caveat is cost, as the current cost of electricity is significantly more than natural gas per equivalent energy unit. The spark gap, as some have termed it in a power generation context, becomes less relevant as the focus is net zero emissions.
Thus, the question of guiding principles in this context starts with the electrification of heating — the north star in the constellation of net zero audit principles.
Heating electrification and a renewable energy principle
With the north star established, its useful to return to the basic steps of energy management:
- Minimize energy (heat) demand.
- Increase efficiency.
- Recover waste heat.
- Investigate and deploy renewables.
These can be used as a framework for the development of net zero audit principles. What becomes immediately apparent is the deployment of renewables as the last step. In an ASHRAE audit, renewables may not be a consideration and historically valued engineered out of the project at final budget. Thus, a major revision to the ASHRAE audit is starting with and prioritizing the investigation of renewable, low- or zero-carbon energy sources that becomes the second guiding principle.
Renewable, low- and zero-carbon energy sources
Because net zero audits must provide a pathway to the decarbonization of building heating, the energy source must be renewable, low- or zero-carbon.
Questions to ask include:
- Is the building siting, typology and heat demand more suited for ground source, air source or sun source?
- What is the heat demand, and are there process heat demands (e.g., swimming pool) that are additive and/or seasonal?
- Is there an opportunity to split and supply the heat demand across different sources? Perhaps combination of all of the above?
Is there a solar-ready rooftop that can support and contribute to a net zero-carbon solution to a process heat load?
In the case of ground source energy for a geo-exchange system, cost and site limitations may have already predetermined the size and capacity of the borehole field.
In the long term, is there a planned district energy system that can serve building heat demand using biomass boilers and the “Zero Over Time” guide created by the Rocky Mountain Institute?
The choice of optimal renewable energy sources — whether at a district or local scale — to decarbonize building operations can become complex especially if done in phases due to capital upgrade cycles. These energy source(s) need to be coordinated with the redesign of the heating system. The coordination of sources becomes the third guiding principle, and heating system redesign the fourth principle.
Heating system redesign to achieve net zero
According to the International Energy Agency, Energy Efficiency 2021 (for buildings, transport and industry), “Energy efficiency offers some of the fastest and most cost-effective actions to reduce CO2 emissions.” Some questions regarding efficiency and heating system redesign include:
- Is there is a way to reduce heating demand through building envelope modifications?
- Can the existing heat distribution system be modified to be more efficient?
- Is heat being generated (in a process) that is wasted and can this waste be recovered for heating demand?
For the first and third, the benefits are clear. For the question about heat distribution systems, there is underlying notion of minimizing the delta between room temperature setpoint and heating loop temperature. Historically, design practices, perimeter radiators and air handling coils were sized for a high-temperature heating loop and a boiler plant — the energy source — would be sized to deliver on these conditions. Starting with this high-temperature loop essentially predetermined the heating system design.
To lower the heating loop temperature, terminal units will need to be resized to maintain net heat transfer. While this adds cost to the net zero pursuit due to the increase in radiant surface area, it reduces distribution losses because the temperature difference between the insulated piping and surrounding air temperature is lower, thus reducing the rate of heat loss. Another benefit is the increase in radiant heat that heats objects — instead of air — thereby increasing thermal comfort.
Another strategy might be rezoning heating systems to reduce thermal demand for zones that are not required to operate on the same schedule as other zones. A common example is a mixed-use building where office floors do not have the same heating and cooling schedule as perhaps ground floor retail and/or restaurants. The net effect of this zone separation is the ground floor can be served by a dedicated heating and cooling system while the office floor system is no longer tied to ground floor operations and can operate less, thus reducing energy and emissions.
In an energy audit, this kind of decoupling of dissimilar zones and introduction of new systems would likely not be considered because it would be cost prohibitive. However, in a net zero audit, the minimum recommendation is to investigate rezoning.
To further assist the energy source and also eliminate natural gas use, the question of energy waste and recovery is another potential measure for the auditor. Recovery in an energy audit versus recovery in a net zero pursuit is akin to comparing apples to oranges, at its core heat recovery might be similar but the nature of recovery needs to be integrated at a system level.
In the example of using cooling loads in the heating season, there is an opportunity to recover condenser water heat instead of rejecting it into the low-temperature return loop. There also is a way to recover washroom exhaust into this loop using a coil.
While the heat recovery distribution system may be costly, there may be limitations on the renewable energy source especially in the case of ground or air source so this source needs support as much as possible so that the overall system can satisfy heat demand for code compliance and perhaps improve thermal comfort.
How can net zero be achieved?
Using the guiding principles below, the auditor should evaluate the feasibility of lowering the heating loop(s) temperatures, rezoning systems and system level integration of heat recovery:
- Electrification of heating.
- Selection of renewable, low- or zero-carbon sources.
- Coordination of sources with heating systems.
- Redesign of heating systems.
Using this “retemp, rezone and recover” approach would lead to a schematic redesign of the heating system to provide the necessary conditions through which the energy source with its potential limitations is able to meet code and comfort conditions.
Further, it should be noted that an iterative approach (versus stepwise) may be needed for everything except electrification to arrive at schematic design cost options that are able to meet budget constraints.
In general, cooling systems are already electrified and thus low-emitting in our market context. However, there are opportunities for cooling integration with heat pumps. This integration is especially compelling if the cooling adds enough electrical demand to the building to put it into a different rate class that reduces costs as in the case of the Ontario market.
This scenario may be an opportunity for energy storage to further take advantage of these rates. If the facility is planning to add more electric demand (e.g., electric vehicle charging stations), this can also be accounted for in the audit and may further the case for electrification from a billing perspective; especially if billing from the local utility is similar to the Ontario market.
A useful criterion for comparing low and zero carbon options is the ratio of the option’s capital cost divided by greenhouse gases reduced. To be clear, life cycle cost and emissions should also be integrated into this ratio. While not the only criteria, the ratio can inform a “red, yellow or green light” decision.
There is an option to reduce electricity demand from receptacle or plug loads of a building, especially in the case of an office tower with a data center that can be the largest part of the energy end-use pie. There are a number of strategies that can be investigated, including virtual servers. Whether there is a data center or not in the net zero pursuit, this reduction is meant to avoid or minimize an electrical service increase that isn’t attributed to an increase caused by the electrification of heat. An electrical service increase is likely and may add significant costs, thus, it is recommended a cost investigation be undertaken as this cost may drive the decision-making process of the audit.
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