Understanding an Anomaly – Part 4 – The A-Ha! Moment

Well, I’m back!

I thought I would have this posted sooner but summer and technology intervened. Right after my last post, I headed to the Oregon coast with my bride, my grandson and his Mom and Dad for a week of playing with “doolbozers”;

building “skyschlapers” just like the one on the current CSE issue cover;

and chasing waves.

We had a pretty good time; the first night there, Jakie (my grandson) came up and hugged me before he went to bed and said “thanks for the beach Gwanpa”.

Even thought I didn’t have much to do with creating the beach, (maybe a bit to do with trying to preserve it), it still makes you feel pretty good. It also tends to remind you that no matter how much love to do what you do for an occupation, there are other rewarding and very important things to do out there.

Anyway, I intended to post again as soon as I returned, but I started to install a new printer which has turned into a technical adventure (as in nightmare) from which I am still recovering. At least, as of last night, I can use my computer again; the new printer; not so much yet.

In any case, you will recall that I have been discussing my initial assessment of a lab facility on the Oregon coast where the site energy consumption and costs had gone up after a retrofit that replaced electric heat with gas heat. Typical expectations after such a retrofit are that costs and consumption will go down.It was this unanticipated, puzzling result that caused the Owner to retain my firm to assess and retrocommission the facility and regain control of the site’s energy consumption.

Initially, I was puzzled too. My average daily consumption analysis revealed that electric consumption dropped when the new boilers were installed and the electric heating equipment was decommissioned, just as anticipated. In a similar vein, I also observed the inevitable increase gas consumption associated with the new boilers coming on line. The key to the puzzling increase in operating cost and site energy consumption turned out to be related to the nature of the heating equipment that was decommissioned and the cost of electricity vs. gas for the location.

It turned out that the original electric heat for the site was provided by heat pumps, not straight resistance heat. This meant that for every unit of energy that crossed the site in the form of electricity, 2, 3, or 4 units of energy were delivered to the facility in the form of hot water.

In contrast, for the new boilers operating at a nominal efficiency of 80%, for every unit of energy that crossed the site boundary in the form of gas, only 0.8 units of energy were delivered to the facility in the form of hot water. The result was an inevitable increase in the amount of energy crossing the site boundary from the utility system, as illustrated in the graph below.

Compounding the problem was the relative cost of gas and electricity at the location. The electricity is provided from a local public utility at a cost in the range of $0.04 – $0.05 per kWh, a relatively low cost, even for the Pacific Northwest (in Portland, Oregon, a similar sized facility would probably be paying $.07 – $.08 per kWh; I pay about $.10 – $.12 per kWh at home).

Gas costs are more comparable with rates through-out the area; approximately $1.20 – $1.30 per therm. To break even in terms of operating cost, electric prices would have to be in the range of $0.11 – $0.12 per kWh with no change in gas cost. Electric rates like these exist elsewhere in the country, but not in Oregon, at least not currently.

Had the original electric heat source been straight resistance heat, then the result in terms of operating cost would have been much different and more in line with common wisdom. To provide a btu of heat in the hot water system via resistance heat, a btu of electricity would have been required. With out the “amplification”, if you will, provided by the heat pumps, an electric resistance heat based system would have used 2, 3, or 4 times the electricity that the heat pumps used with 2, 3, or 4 times the cost.

In the next post, we’ll take a look at the reason why a btu of heat from an electric resistance heating system is so much more expensive than a btu of heat generated by burning a fossil fuel on site. The answer is related to the difference between site and source energy, which is also the silver lining in energy consumption cloud that was hanging over the lab facility.

David Sellers
Senior Engineer – Facility Dynamics Engineering

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