Reduce Gas Bills with a Boiler Outside Air Reset

Can’t help but slam your fist looking at ever-increasing gas bills?

PulseIQ can help you navigate this maze and explore different options to save energy costs for your boiler system. One way you can save over $3,350[1] every year is with Boiler reset and Cut-Out Control.

A Boiler reset based on Outdoor Air Temperature (OAT) can help you reduce your Gas bills by about 5% [2]. Essentially, when the OAT rises during the day, the heating demand falls so we can run the water a little cooler. Similarly, when the OAT drops at night, we can run the water a little hotter [3]. Doing this ensures your Boiler works a little less, translating to gas savings which quickly add up – especially during the shoulder months. Further to top it off, using a Boiler Cut-out control and preventing a Boiler from turning on when the OAT is above a specified temperature can save you another 2.2% [2]. Most mechanical contractors simply set a Boiler reset schedule by programming a hot water range to say 140 °F to 180 °F against an outdoor air temperature range 60 °F to 20 °F [4]. This, while functional, is not ideal.

In a residential building, it is easy to end up in a situation where the internal load can be both high and relatively constant. In such a case, if we employ a Boiler reset based on OAT and decrease the supply temperature during a hotter time of the day, we will end up underheating the space (or vice versa in the cooling season using chilled water reset based on OAT). This is because we are looking only at the outside conditions and not the conditions in the apartment themselves [5]. Such a reset will not maximize your savings or the comfort of your resident’s comfort.

Similarly, return water temperature is also a poor indicator of demand. It is the average demand across all the fan coil units and will not be indicative of whether we have poor cooling or heating across some coils [5]. Further, the presence of any faulty 3-way values can cause Low Delta T syndrome and further throw you off.

At PulseIQ, we always conduct a brief baseline study to understand the building’s load profile. By looking at Time of day, Occupancy, OAT, and using our proprietary thermostats to understand Zone loads, we can optimize for tenant comfort and Boiler’s energy consumption to the maximum extent possible using conventional rule-based controllers.

Let’s look at a scenario where this is in action.

In figure 1 and figure 2, we have a real-time plot of Building supply temperature and OAT for two different properties in Washington DC.

In figure 1, we can see that the building supply temperature trend is a mirror image of the OAT. This is expected when your Boiler Outdoor air reset is working properly.

Figure 1 – Site 1 – Boiler Reset present and working as expected

In figure 2, we can see the building supply temperature maintained relatively constant at about 150 °F despite the changing OAT.

Figure 2 Site 2 – Boiler Reset absent

For a Boiler with a capacity of 2.8 million Btu/hr, this would mean a saving of $3,355[2] in gas costs per year with just a simple OAT reset and Cut-Out.

References


[1] U.S Energy Information Administration, “EIA forecasts U.S. winter natural gas bills will be 30% higher than last winter,” U.S Energy Information Administration, 25 10 2021. [Online]. Available: https://www.eia.gov/todayinenergy/detail.php?id=50076. [Accessed 30 11 2021].

[2] Shelter Analytics, “TRM,” NEEP, 2020.

[3] Energy Solutions Center, “Boiler Reset Control,” [Online]. Available: http://cleanboiler.org/learn-about/boiler-efficiency-improvement/efficiency-index/boiler-reset-control/. [Accessed 30 11 2021].

[4] Pacific Northwest National Laborator, “PNNL Building Re-tuning,” 9 2020. [Online]. Available: https://buildingretuning.pnnl.gov/retuning_measures.stm. [Accessed 30 11 2021].

[5] R. Seidl, “Using Demand Based Reset Strategies,” in National Conference on Building Commissioning, 2008.

[6] J. Dice, “Nexus Newsletter,” 9 11 2021. [Online]. Available: https://www.nexuslabs.online/blog/.

 

[1] Capacity = 2,87,300 Btu/h, EFLH = 1,587 hrs., 0.85 $/Therm

[2] Capacity = 2,873,000 Btu/h, EFLH = 1,587 hrs., 0.85 $/Therm

"*" indicates required fields

This field is for validation purposes and should be left unchanged.