• Getting to Green

    An administrator pushes, on a shoestring budget, to move his university and the world toward a more sustainable equilibrium.


Issues of scale

To attend a commencement last weekend, I had to travel overnight. Two related observations stick in my mind, although I haven't entirely figured out how to address the information they offer.

May 19, 2009

To attend a commencement last weekend, I had to travel overnight. Two related observations stick in my mind, although I haven't entirely figured out how to address the information they offer.

First, in the motor hotel room, the through-the-wall ventilation unit wasn't an air conditioner but a heat pump. That is, during heating season, the thing can be run "in reverse" to pump heat from the cold outside into the relatively warm room. Since the commencement was within a day's drive of Backboro, sometimes the temperature difference can be extreme. Thus, at times, the heat-pumping mechanism would be replaced/supplemented by electric resistance coils (never an efficient heating mechanism).

Second, on the drive back, I noticed a large number of trailers parked by the side of the highway in a stretch of road which was labeled as a construction zone. Each trailer had a generator and a couple of high-pressure lights mounted on a mast -- their obvious purpose was to provide an unbroken swath of light to allow night-time road construction.

The decision to install individual heat pumps in every room of a hotel/motel is easy to understand. First, the unit itself costs only a little more than a straight air conditioner (which you need to install anyway). If it consumes an inordinate amount of electricity during heating season, at least it only does so when that room is occupied (and thus the cost can be covered by room rental income). Having the heat pumps means that the central heating system can be sized precisely to handle the lobby, hallways and other common areas, not a variable amount of space depending on how many rooms are occupied. The energy savings from being able to right-size the central system could possible exceed the energy wasted when those inefficient heat coils fire up.

The use of many small diesel generators to power night-time construction lights, however, seems simpler to analyze. Hotel rooms might be occupied or vacant on a room-by-room basis, but whole construction zones are generally either active or inactive. (I much more often see a mile of highway lit up even though the crew is working in only a hundred-foot stretch than I see only the couple of closest units operating and the rest dark. Truth be told, if I were a highway construction worker on a night shift, that's probably the way I'd want it, too.) But if forty or fifty pairs of lamps need to be lit up all night, operating an identical number of small generator units is a really wasteful way to do it. Far more fuel-efficient to have one or two big generators and cables stringing the masts together so all the lights get power.

In terms of the construction lighting, I'm thinking that scalability (use just that number of units you need to solve the size of problem you've got) is of benefit to the people who administer the equipment rental process, but ecologically irresponsible and probably more expensive than it needs to be (even in these days before cap-and-trade). In terms of hotel heating, I'm thinking that a similar scalability characteristic is pretty much a push -- not much of a win, but probably not much of a loss, either.

Both of those conclusions are a wee bit surprising to me, as on other fronts I've thought of scalability achieved through small granularity as a common characteristic of sustainable systems. Maybe these are just the exceptions which prove my rule of thumb.

Or maybe my thumb needs to get itself a better scalability rule.


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