Right sizing makes a difference

Two recent REG projects involved reviewing the sizing for mechanical equipment—one for a cooling system, and one for a heating system. In each case, our load calculations allowed us to downsize the system and save money for the owner—almost two thousand dollars in the first case, and over a thousand dollars in the second case.

In the first project, a mountain-town art gallery with east-facing windows was getting blasted by morning sun, making the space uncomfortably hot by the mid-afternoon. The owner had window ventilators, but outside air can’t help you stay cool when it’s over 80F outside. We considered—and rejected—low-energy options such as night precooling (not enough active thermal mass, and space would be too cold in the morning), evaporative cooling (nowhere to install the equipment, which is very efficient but rather bulky), radiant cooling (no tubing in floor, no reasonable source of cool water), and load reduction (internal loads were already reduced, and window films would reduce gallery visibility from the street).

 

In this situation, the only remaining option was “real” air conditioning via a split system. The mechanical contractor that engaged REG for the job was debating between 3-ton and 4-ton systems. With only a couple of hours of engineering time, we were able to convince all parties that a 2-1/2 ton system would get the job done. This selection saved nearly two grand and allowed the smaller equipment to fit better into the tight spaces.

The second project involved new boilers for a 15-year-old affordable housing complex with 31 units. The old boilers were less efficient than modern equipment, and each apartment had its own electric water heater—not the most affordable option for affordable housing. This time the name of the game was domestic hot water—a.k.a.DHW.

 

 

How much hot water do you need for 31 apartments? It turns out there are several ways to look at this problem, but to be realistic you have to account for diversity (the fact that not everyone will take a shower at the same time.) We looked at a peak hour of DHW demand in the context of a three-hour window in the morning where the most use tends to happen. Our analysis showed that we could amply meet demand with a combination of three storage tanks and two boilers, one of which was downsized from the original size selection. Cost savings was just under one thousand dollars, even considering upgraded variable-speed pumps for the new heating plant.