Following on the thread here at iBratt concerning energy efficiency at the West Brattleboro fire station, this article is on life-cycle cost analysis as an alternative, many would say better, decision making tool for major capital expenses like fire stations. Versions of this should appear in the Reformer and Commons soon as well. Info on assumptions, modeling tools, etc. will be added in the comments section.
The (truer) Cost of Things (like buildings)
When a large building is built the owner usually bends over backwards to keep construction costs as low as possible. What would happen if the primary objective were not to minimize up-front costs but rather to keep the cost of operating the building over its lifetime as low as possible? This is called a life-cycle cost analysis. Let’s apply it to the West Brattleboro fire station that is currently under construction, in particular its heating energy use.
Through the marvels of computer modeling we can estimate the amount of energy a building will use to stay warm. One only needs to know what the wall structures are going to be, how many windows and doors of what sizes, the insulation levels that are proposed and how ‘tight’ it will be from an air leakage standpoint. The WB fire station is being built with insulation under its floor of R-10, wall insulation of R-25 and ceiling insulation of R-60. If we had upgraded these levels to R-20, R-45 and R-60 respectively, installed better insulated windows and doors, and improved the building’s tightness from 0.5 air changes per hour (per sq. ft. of building shell – the maximum allowed by code) to 0.2 air changes per hour, the town would save about $1,600 per year at today’s cost of $1.59 per gallon for propane. These higher levels of insulation and air tightness are what the green building industry considers ‘best practices’ or ‘High-Performance’ building standards.
Judging from the many years’ worth of deliberation and hand-wringing that it took for the town to make the decision to rebuild its police and fire stations it seems like a good bet that these buildings will be used for 50+ years. If we project the savings out 50 years and make an assumption that energy prices will inflate by 3% per year, the lifetime savings for building the WB fire station using best practices would have been over $180,000 to the town of Brattleboro. Of course we have no idea what energy prices will do in the future, but we can assume a few things: 1) the building will be heated, 2) the heating system that is being installed today has a 20+ year lifespan, 3) the insulation that is installed in this building today will be there for the rest of the building’s useful life, and 4) energy prices are near historic lows today and few people think they will stay that way for long. If energy prices jump back to where they were a couple years ago the lifetime savings would dramatically increase with a high performance building.
The WB fire station’s designers might argue that they have exceeded code in the design of this building, and thereby saved the town money. This is true. If we model the building as designed and compare it to a comparable building built to code (R-10 below slab, R-20 walls, R-40 ceiling, 0.5 air changes) the life-cycle savings over 50 years is estimated to be $10,000. Building codes define the minimum allowable building practices, the lowest end of the spectrum of possibilities. The building as designed is still going to cost the town substantially more over its lifetime compared to an identical building that is built using best practices.
Let’s do another modeling exercise here. Let’s assume that the building is built as designed, but instead of a propane boiler the building is heated with a heat pump, and that the electricity used to power that heat pump comes through the deal that is being offered from the Windham Solid Waste Management District’s landfill solar project, with prices locked in for 20 years then rising at 2% per year for the next 30 years. The savings over 50 years for this single change would be even more than above, roughly $214,000. In addition, 650 tons of greenhouse gasses would have been avoided.
Last year the town energy committee, at the instigation of then chair Lester Humpreys, recommended that the Selectboard adopt a policy of making all major capital expenditures using a life-cycle assessment of costs. The analysis presented here is rudimentary and simplified to make the concepts understandable to a layperson. Rigorous life-cycle cost analyses should include a more extensive set of costs and savings, such as the additional cost of heat pumps and more insulation, the savings from being able to downsize heating equipment and the substantial benefits of having buildings that are more comfortable and resilient to power outages. I would urge the Selectboard and relevant committees to instigate such analyses for all major building projects, especially the police station and central fire stations that are still in the design phase. I would also urge the town to specifically consider making these buildings High Performance structures that are heated either with heat pumps powered by a solar array or modern wood heating systems, whichever saves the town the most money over the long haul.
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Tad Montgomery is the principal of Home Energy Advocates. He sits on the Brattleboro Energy Committee and Windham Regional Commission Energy Committee. Steve Lloyd, retired architect, helped with the energy modeling for this article.
Background Information
The program used to do this life-cycle analysis (LCA) was a spreadsheet-based modeling software called Q-Loss. Experts in modeling were enlisted to help with the analysis.
Eric or someone on iBratt asked about specifics. Window U-values (the inverse of R-value) were improved from .32 (planned) to .29 (our ‘best practice’ assumption) which represents improved double-pane windows. We didn’t think the town would spring for triple-pane as the payback can be 30 years+.
Door R-values were improved from 3 to 8.
The big bay doors for the apparatus were improved from R-10 to R-15.
Wall and window areas were all measured from the architectural plans. There are really two buildings there: the apparatus bay and living/office quarters. These areas will be kept at different temperatures and have an uninsulated wall connecting them. This makes modeling a bit difficult. We assumed that the apparatus room (79% of total volume) would be kept at 60°F during the winter, and the other rooms (21% of total volume) at 70°F. To model this we assumed an average temperature of 62°F for the entire building.
For the heat pump (air-to-water) we deliberated at length about performance. One expert suggested we use a coefficient of performance (COP) of 2.3, another said to use 2.8. Since heat pump performance has consistently improved over the last couple of decades we assumed that it would continue to improve over the next 50 years as the building’s heating systems are upgraded, and we used a conservative number in the middle of 2.65 [COP represents the ratio of heat energy gained to electric energy input].
Propane hydronic heating is proposed for the entire building. We assumed that a high-efficiency model is planned, with an AFUE (efficiency) of 92%.
There may be inaccuracies in some of these assumptions, we did the best we could with the information we had. For example, we have no information on the costs of the improvements needed to achieve a high performance building. A comprehensive LCA would be done over a number of iterations with different assumptions and better data as the design is refined. The goal would be to incorporate all of the different building energy systems into the analysis with the objective of minimizing the lifetime cost of constructing AND operating the building. If done properly the cost of financing the high performance building improvements are more than offset by the lower energy costs.
There is a risk that energy costs will remain low, and savings projections will not be realized. The assumption or ‘bet’ that energy prices will increase is wonderfully hedged, though, in that the town will benefit financially overall from low energy costs if prices stay low. If energy prices skyrocket the town would be well insulated from price shock with high performance buildings.
Tad
I have a few more questions
I have a few more questions but no time to ask them now, I’ll post later. I wanted to make a suggestion, in case you hadn’t submitted this for publication yet.
It would be super helpful, when you say an $1,800 savings per year if you provided the full yearly fuel cost of scenario A and B. That gives folks an idea of whether we are looking at a 5% savings or a 25% savings.
I would also recommend adding a sentence with the same scenario A and B annual fuel costs but using an example fuel cost from the higher-priced years we saw a few years back, and will likely be returning to.
I’ve learned not to trust people to do the math themselves, lay it out for em.
Just my $.02. Hope you don’t mind…
(P.S.) It may not be too late to spec heat pumps? Are they installing separate cooling or will the building have no A/C?
Do you know if this was ever discussed as a possibility during the design phase or did the architect fall aslseep at the job with the mechanical design like they did with the vapor barrier?
a few more answers
The buildings were modeled to use 175 MMBtu/yr (million Btu’s per year) as built and 91.2 MMBtu/yr with best practices. I used a figure of 92,500 Btu/gal. for LP gas. This translates to 1,900 and 991 gal. of propane used per year, respectively. This year’s cost to the town is $1.59/gal. If the price of propane doubled to where it was a couple years ago, the savings would be $3,200 per year for the town.
I did not get into cooling loads, or heat recovery ventilation, in this analysis. Thy should both definitely be considered in a comprehensive LCA.
I have no idea whether it is too late to change the heating system to heat pumps. I and others on the energy committee proposed numerous times that these technologies be considered, as well as pellet systems, and eventually gave up.
My understanding is that the Brooks House is heated with a central air-to-water heat pump.
Ventilation
Do you know what they are intending to use for ventilation? Specifically in the garage area?
Are they going to use an HRV/ERV or are they just strapping a big ol fan to the wall and going exhaust only? (Is balanced too much to hope for?)
I’m looking at your air change numbers and trying to figure out the best way to account for Steve Horton’s contention that the fuel savings of extra insulation are insignificant compared to how many air changes having those big garage doors open frequently will cause. But, no idea how often they will be opened in the winter and how long they are kept open.
I’m assuming the ventilation will be significant though, with engines running indoors, unless they intend to rely on the open garage doors?
Has an HRV been discussed anywhere in there? Do they even work in this application?
Ventilation
The plans show two big louvers on the rear of the building, I saw nothing that mentions heat recovery in the ventilation.
I wasn’t there for the comment you attribute to Steve Horton, but the apparatus doors are going to be open the same amount whether the building is built to code or Best Practice levels. This energy loss coming through the open doors is separate from, and independent of, the energy loss through the walls and other air leakage pathways in the building. It’s apples and oranges, so to speak.
I was present at a Selectboard meeting where Steve said that they had gone to R-60 in the ceiling “because heat rises” and this is the most cost effective place to insulate. This statement confused me – heat doesn’t rise, heat moves through three primary mechanisms – conduction, radiation and convection. Hot air rises, in certain circumstances, but that’s irrelevant if the building is built using good air sealing techniques. To say that the ceiling is the most important building element to insulate is like saying that wearing a warm hat in the winter is the most important thing – slippers and thin, cotton sweat pants are just fine for the lower parts of the body. This was borne out in the modeling, which showed a mere $10,000 benefit over 50 years for upgrading from R-40 to R-60 in the ceiling. Energy flow is not a linear effect of insulation values, but that is perhaps TMI.
I would just finish by stating that I think Steve is a good person and has handled most of the aspects of this difficult and highly complex design project pretty well.
Background Information II
Milt Eaton, who sits on the Bratt Energy Committee and works in the field of energy on the national level, asked how long into the future I planned to do the projections. I said 50 years, as that’s how long I expect these buildings will be used by the town, judging from past experiences with police and fire stations here. He replied “I wouldn’t go out more than 10 years, as we really can’t project energy costs or technologies accurately out further than that.”
I showed the article to another friend who manages one of the big science buildings at UMass. His main comment was “Do you really think that these buildings are only going to be used for 50 years? Why not project out 100 years? Are they being built to last 100 years?”
I pondered these statements for a long time, and think that there is some real wisdom coming from both angles. To not project out for the entire useful life of a building seems to me to do a disservice to the town and our decision makers because it essentially implies that the decisions that we make today will not have an impact more than 10 years from now, and few would believe that this is true. A comprehensive LCA might do a series of projections with different time spans used and different degrees of certainty.