Ever notice how new words or phrases continually slide into our social vocabulary? Here are a few examples that pertain to energy and buildings: Sustainability, energy justice, climate justice, beneficial electrification and decarbonization.
Some of these terms are quite “malleable” when it comes to their intended meaning. “Climate justice” is one such term — at least for me. Ask ten people who frequently use this phrase in their writings and presentations exactly what it means, and I suspect you will get quite a range of answers depending on each person’s world view, career position and political inclination.
Another contemporary term that’s currently popping up in a variety of communications involving buildings and energy is “resiliency.” It’s meant to convey the concept that buildings and their associated environmental control systems should be able to maintain near normal operation under abnormal conditions such as extended power outages, temperature extremes, strong storms or supply chain interruptions. Resiliency is a very desirable and rational concept.
Not there yet
Think back to the winter of 2020-2021. A strong polar vortex storm caused massive damage in Texas, knocking out power for weeks in some locations and creating sub-zero temperatures in the Dallas/Fort Worth area. That storm started a domino effect leading to frozen pipes, natural gas interruptions, inoperable sewer systems and intolerable temperatures in tens of thousands of homes and commercial buildings. This event and its aftermath demonstrated an abysmal lack of “resiliency.”
The aspirations of those who advocate for a complete and expedited switch from fossil fuel in favor of complete electrification of HVAC systems sometimes overlook situations that are inherently resilient. One example is a belief, by some, that existing fossil fuel heating systems — such as boilers fired by natural gas, fuel oil or propane — should be scrapped ASAP and their function replaced by an electrically-driven heat pump with electric resistance backup heat. This concept is short-sighted from several perspectives.
First, assuming that the boiler is functional, serviceable and has been adequately maintaining comfort in the building, leaving it in place allows for non-electric supplemental heating. This helps reduce the emerging peak power demand scenarios that many electric utilities will soon face as more and more buildings go over to all-electric heating. It also reduces demand charges in commercial buildings.
Based on simulations I’ve been working on, an air-to-water heat pump could provide between 70% to upwards of 97% of the total seasonal heating energy in a home equipped with hydronic heat. The lower end of this range corresponds to buildings in very cold climates equipped with legacy high-temperature hydronic distribution systems. The upper end corresponds to lower energy use buildings, in less severe, but nonetheless “cold” winter climates, using low-temperature hydronic distribution systems (e.g., design load supply water temperatures no higher than 120° F). There are many factors that collectively determine just how much of the seasonal space heating energy can be supplied by the heat pump, but the takeaway here is that the majority of this energy is supplied by electricity rather than on-site fossil fuel.
Second, leaving the existing fossil fuel boiler in place allows for full capacity backup if the heat pump is down for service. Granted, heat pumps have improved a lot since their introduction in the 1970s. Still, modern heat pumps are a complex assembly of electrical and mechanical components, many of which are separated from the outdoor environment by little more than a sheet metal cabinet. It’s unrealistic to think that any device of such complexity, and operating in an outdoor environment, will make it through 15-20 years of operation without a single service issue that will temporarily shut it down. If it’s the sole heat source for the building things are likely to cool off before it can be put back in operation.
Third, most fossil fuel boilers and their associated distribution systems can operate on a few hundred watts of emergency power. A small and relatively inexpensive portable generator could keep most fossil-fuel heating systems in residential and light commercial buildings operating during a prolonged power outage. Buildings with heat pumps and electric resistance backup can also be maintained by emergency generators, but typically require much larger and more expensive units. Think 20 kW capacity instead of 2 kW capacity.
Customer-side battery storage systems, such as the Tesla PowerWall or Generac PWRcell also have the capacity needed to power a typical fossil-fuel boiler for several hours during a utility outage.
Fourth, the combination of a heat pump (air-to-water or geothermal water-to-water) with an existing fossil fuel boiler provides time-of-use flexibility. The fossil fuel boiler could be used at times when peak electric rates are in effect, or times when utilities experience peak demand and need to shed load through pre-established agreements with specific customers. The heat pump could be operated during “off-peak” times (e.g., nights, weekends and holidays) when the cost of electricity is lower. This “dual fuel” flexibility is also synergistic with future utility strategies such as “real-time” pricing.
Fifth, there’s obviously a cost associated with removing a boiler and its associated piping, fuel supply system, wiring and venting. Why add that to the upfront cost of installing the heat pump?
Keeping a functional fossil fuel boiler in a system as a secondary heat source to a heat pump provides a transitional strategy toward increasing electrification. This approach helps buy the time needed to implement electrification without over-stressing existing power grids and peak generating capacity. It also defers the need to upgrade electric service entrances to accommodate heat pumps combined with electric resistance backup heat. When an air-to-water heat pump or geothermal water-to-water heat pump is added to an existing system, small piping modification can be made that would allow an electric boiler to eventually replace the fossil fuel boiler without major system reconfiguration.
We’ll get there
I’m not against properly planned electrification. I’ve certainly tipped my hand on this through many past columns dealing with renewable heat sources, air-to-water heat pumps in particular. The eventual transition to heat pumps is a huge opportunity for the North American hydronics industry, probably the biggest that I’ve witnessed in over 40 years.
However, I’m also a “realist” in terms of rushed, rash, or sweeping policies that overlook favorable opportunities. Fossil-fuel should not be treated as “public enemy No. 1.” Its use is the reason for the comfortable, convenient and arguably luxurious lifestyle most North Americans enjoy in comparison to much of the world’s population.
The percentage of renewably-generated electricity that flows into the grid is growing every year. The global societal and political forces that are now steering the HVAC market toward electrification are powerful. They are beyond what any individual or corporation can control. They represent a “breaker” ocean wave. Those in the hydronics industry have a choice of either being crushed by that wave, or riding it all the way to the shore. Heat pumps combined with modern hydronics technology are the “surfboard” for those who choose the latter.
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