MANY OLDER apartment complexes, which were built more than 30 to 50 years ago, are coming up for major boiler and component replacement. Unfortunately, in most cases, we as contractors go into the job with a “replacement system” mindset. This means that we see what has been there for the last 30 or so years, and we replace it with similar components.
Sometimes we, as mechanical contractors, take too many things for granted. Such as, “They don’t want to spend any more money than necessary, so I won’t bother talking to them about boilers with substantially higher seasonal efficiencies.” Or, “This system has worked fine for the last 30 years, so why should I try to change the configuration?”
We get stuck in the rut of life, and we ignore the fact that some of the newer technology that is currently available offers substantial energy-saving potential. We get so used to being the “boiler replacement men” that we can’t see the forest for the trees.
Look around you, my friend, and ask lots of questions. The answers might surprise you.
I was recently asked to take a look at an older apartment complex heating system. All the local experts had already looked at it and told the owners it was as efficient as it was going to get. The owners thought otherwise.
The savvy landlords had been analyzing their other properties and comparing fuel consumption per person and per square foot for all their buildings. They noticed that this property was way out in left field in terms of energy unit per person per square foot. They asked me in to take a look at the system.
When I examine one of these systems, I look everywhere, not just in the mechanical room. I ask lots of questions of the people who live in these buildings. I ask questions of the person who has been in maintenance and daily management too. Unfortunately, the maintenance and management end sometimes has a high turnover rate, so I might get answers that are vague at best and not qualified by real on-site experience.
I also look at the end use of domestic hot water (showers and lavatories) and the space heating distribution systems, because we often overlook potential energy savings there.
Look at the distribution system and think “insulation.” In some cases, this may not be possible because the pipe is inaccessible. Such was the case with this property.
The system was set up like a district heating system. It had a centrally located boiler room with two 5-million-Btuh water-tube atmospheric boilers, two humongous shell-and-tube heat exchangers for domestic hot water, and all the distribution lines were run to the outlying buildings underground, un-insulated.
Now, obviously, the job of digging these lines up and insulating them would be a daunting task at best, but it also means that there is a lot of energy conservation potential in doing an outdoor reset on the systems. Note the use of the plural word “systems.”
Within this and many other boiler rooms, there are many different systems. We have the heat source or sources, the circulation system for the space heating portion, the DHW heat generators, the DHW distribution system and the DHW re-circulation system.
Energy can be saved with each of these “systems” based on being able to turn down the system during periods of little or no demand. Let’s look at the DHW portion first.
In the case of the dinosaur in question, the DHW was being provided through two shell-and-tube heat exchangers. The two 5-million-Btuh boilers generated heat for the heat exchangers. The boilers have been kept in a 180°F, ready, steady state of operation for more than 25 years.
That’s the way they did things back during the cheap energy era. The standby losses of the two boilers and the distribution system alone were greater than the actual load on the system!
Why would they keep these large boilers idling at 180°F? Simple. “You never know when someone is going to use DHW, and you never want to run out of DHW.”
So, to avoid that, you keep the boilers running at their maximum operating temperature. Not a very efficient way of operating a system during the summer, eh?
What’s really sad is that the actual major loads imparted to the DHW system typically only last for about two to three hours per day, depending on the type of occupancy, and they are extremely predictable.
At a minimum, the system could have been programmed using time clocks, aquastats and simple outdoor reset controls.
During off-peak periods (middle of the day and middle of the night), the DHW temperatures could have been turned down from their normal peak operating temperatures and the boilers also turned down based on the outside temperature. During peak use periods (5 to 7 a.m. and 6 to 7 p.m.) the temperatures could be turned back up to handle the peak demands.
This procedure usually requires the introduction of a good-sized (119-gal.) storage tank on the DHW side of things, but it is extremely doable and really improves the efficiency of the system.
Tune in next month as we continue to delve into the workings of these older complex commercial systems. Until then, happy conservation-driven hydronicing!
Mark Eatherton is a Denver-based hydronics contractor. He can be reached via e-mail at [email protected] or by phone at 303/778-7772.