A lot has been written about the technical side of energy efficiency. The human side is usually left out. What managers, tenants and technicians believe matters more than another gadget. These are the myths that get repeated most often, and that waste a great deal of energy.
How mentality drives consumption is a subject of its own, and the effect is large. Related reading: Mentality and energy efficiency. Below, the specific myths.
Myths and stereotypes
A myth usually sits on a scrap of truth, often from another era. Where do they come from?
- Pride. It is hard to drop a belief you already hold.
- Laziness. A stereotype is easier than thinking it through or running a test.
- Lack of knowledge, and repeating whatever a supposed authority said. A service technician, for example.
The designer, the manager and the service tech are never wrong
Even recent papacies have stepped back from the dogma of papal infallibility. Plenty of technical people still treat design assumptions, and old orders from a boss, as infallible. In practice, plant is often oversized. Sometimes the assumptions were wrong. Sometimes they simply no longer match how the building is used. Blindly following the drawing, or the instruction you were given, is usually fear mixed with laziness. Your backside is covered, as people on site like to say, and you are excused from responsibility. In reality you are excused from thinking.
Energy efficiency is not in the direct interest of many of the people involved. They gain nothing from it, and they might get a problem. If someone has no stake in saving energy, why follow their advice blindly? Think. Anyone can be wrong, including me, right now.
Starting equipment up is bad for it
Does anyone leave the car engine running after parking at a shop, or overnight, just because a cold start is hard on the engine and uses a bit more fuel for a moment? Of course not. In some places you can be fined for it. In energy-hungry HVAC, that attitude is still common.
On modern plant, the wear from leaving a machine running is out of all proportion to the wear from a start. A start barely matters. The myth comes from older installations, where starting and stopping every few minutes really did shorten the life of fans without inverters, and of fluorescent lamps. It does not apply, even to that older equipment, when the off period is tens of minutes or hours. On today’s HVAC the energy used at start-up is marginal next to leaving the plant running.
Cycling most HVAC equipment every few seconds, or every couple of minutes, is pointless. Once the gap is tens of minutes, you can, and usually should, switch it off. Some machines are built to change state constantly. Toyota hybrids start the engine for a few seconds at a time and still do a million kilometres. Then comes the next myth: an air handling unit needs half an hour, or several hours, to start, so it should just run flat out. A normal start takes a few minutes, rarely more than ten. Leaving it on “just in case” makes no sense.
Start-up uses a huge amount of energy
The claim is that a start uses far more energy than continuous running. Sometimes consumption is briefly a little higher. Often it is not. The story again comes from the previous era, and it was only partly true. Old electric motors and fluorescent lighting did draw more at start-up, for seconds or a few minutes. A simple measurement on the actual machine kills the myth. What is left is the belief.
In winter it has to run all the time
If a car will not start in the cold, what do you do?
- Fix it.
- Leave it idling all night, because in the morning a cold engine will not start.
Nobody sane leaves the car running overnight. Plant that uses more energy than a car is left on all night as a matter of course. In the morning, when it is cold, frost alarms refuse to let it start. Sometimes it is left running simply from fear that the space will cool down. A normal response is to fix the cold-start problem. In practice, “technical” people recommend 24-hour operation in winter and in summer, meaning almost the whole year. I have had service technicians and in-house techs recommend exactly that. From their point of view it is easier than finding the cause. They do not pay the energy bill.
In our climate, air handling units and similar plant are designed to run normally down to about −20°C. Barring a special case, they should start and run reliably at that temperature.
Night setback uses more heat than it saves
The popular version: keep the heating at daytime temperature all night, because dropping it means you will burn far more bringing the building back up. Does anyone leave a car running overnight because the morning start will use more fuel?
The myth may once have been true in some narrow case, with an old heat source that burned and transferred heat badly. I have not seen that case. For years, heat meters have shown a short spike while the temperature recovers, and that spike is much smaller than the energy saved by the setback.
The free-cooling myth
Deliberate free cooling often does not pay. I mean running the air handling units extra at night. The fans can cost more than the cooling compressors would have, and you add wear: filters, fan bearings and the rest. You also push night-time moisture into the building. In summer, humidity has a lot to do with whether people feel comfortable.
Free cooling that comes along with ventilation you needed anyway is a different matter. So is free cooling that costs nothing, such as stack ventilation through open roof windows.
Fighting myths, not windmills
Stereotypes that harden into myths make life easier, and people do not give up a belief just because someone challenges it. The usual reaction is to defend it and hold on harder. Even if you prove them wrong outright, wounded pride will find a way to pay you back later.
What works better is to skip the direct confrontation. Propose an experiment. Meter readings and the documentation grow the doubt, show the real problem, and produce a number that is hard to argue with. An experiment also gets people thinking for themselves, and beliefs often move without you having called anyone an idiot. Some people will not be moved by hard data. Don’t tilt at those windmills. Go around them.
Polish version: Mity efektywności energetycznej.
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