What Business Are We In -- Emergency Or Comfort?
If you're one of the folks who has to go on service calls in the middle of the night (the coldest, darkest ones, of course), there's no question about it -- you're in the emergency business. And that's not all bad. For one thing, it usually pays pretty well.
But think about it. Emergency is supposed to mean that someone's life or safety is in danger. Do people normally die or get seriously ill from their house getting down to, say, 50 degrees in the few hours before the normal business day begins? When you think about, why couldn't they just put an extra blanket on and wait until morning?
When someone calls and says, "Help! I have an emergency. My heat's out," I think they're really saying, "I'm a total wimp and I'm afraid -- I'm afraid that I'm going to be uncomfortable." No matter how you look at it, uncomfortable is not threatening to life or safety. History says that humans survived just fine for lots of years before we had automatic temperature control.
The Comfort BusinessFar beyond simply providing heat, our job is to deliver just the right amount at just the right time. And we can. The problem is we often don't, maybe because we don't quite understand how.
There are some special considerations about thermostats that can make a big difference as to whether or not you're delivering the most comfort possible. Doing it right rarely costs much more money or takes much more time. It's mainly a matter of knowing.
Almost everyone in the heating business has heard of the anticipator. The anticipator adds a tiny bit of heat during the heating cycle. It tricks the thermostat into thinking the room is just a little warmer than it is, so it shuts down just a little early.
Then the residual, or leftover, heat in the system finishes the heating to just the right temperature. But hardly anyone knows what it does or how to adjust it correctly.
In an electro-mechanical thermostat there's a dial with little numbers on it. The numbers all have a little dot in from of them, which means they are decimals. The numbers are tenths of amps. What you're supposed to do is (pay attention, now!) match the setting on the anticipator with the amp draw of the load in the thermostat circuit.
Every load (a valve, for example) has an amp draw. It's marked on the device itself. Let's say the zone valve says .32A on the end of it. If you set the anticipator at .32, you will then have maximum comfort for the people in the room.
But what does that do? The anticipator adjusts cycle rate. Cycle rate is how many times an hour the heating equipment has an opportunity to come on.
The heating industry standard for cycle rate is six cycles per hour. If you divide 60 minutes by six cycles, you get 10 minutes per cycle. Ten minutes is the standard heating cycle. A cycle is on time plus off time. Six cycles per hour is the industry standard because it's been found that this cycle rate keeps the room temperature within a two-degree temperature swing. That means the temperature may go one degree above setpoint or one degree below setpoint, but no more.
Remember that if the temperature stays within that two-degree range, most people don't notice a temperature change. That's the definition of comfortable. If it changes more, people complain: "It gets hot in here, then it gets cold in here -- it's never comfortable."
Military PrecisionLet's look at the anticipator itself again. Notice that at one end is the word "longer" with an arrow pointing toward that end. As you adjust the indicator that direction, the cycles get longer. Longer cycles mean the heat is on (and off) for longer times. It also means it comes on fewer times per hour. Shorter cycles mean there are more per hour.
People can be quite opinionated about whether longer or shorter cycles are better. Here's a story to illustrate:
One day in early fall I received a phone call from a homeowner who growled, "I've been up all night for the last two nights timing your heating system. I've charted when it comes on and off, and it runs every 10 minutes. That's costing me money and you're going to do something about it." (Guess this guy's profession.)
Fortunately, I'd had a little customer service training, so instead of the many things I could have mentioned I said, "It sounds like you're really upset. But I'm curious. What's your profession?"
"I'm an engineer, and an Air Force colonel," he bellowed. Then he calmed. "Ah heck," he said. "I just retired last month. My wife's been away visiting her sister, I'm bored and I can't sleep at night."
Ah, this all makes sense now, I thought.
"Well, you have my sympathy," I replied. "The industry standard for your heating is to come on every 10 minutes if you need heat. That's six cycles per hour, and that'll give you the best comfort. How often would you like it to come on?
"I want no less than 20 minutes."
"We can do that. Do you have a heating contractor?"
He didn't have one, so I referred him to one who I know enjoys a challenge.
A few weeks later I got a call from heating man Jerry. "Thanks for throwing me to the wolves," Jerry said. "I went out to see that Air Force engineer. I reset the anticipator so he got his 20 minutes. But now I'm getting calls from his wife. She's saying, 'Ever since you've been here, it gets hot in here. Then it gets cold. It used to be comfortable.'"
The engineer military man was happy because things are running to his standard. But his wife, who wants things comfortable, was no longer happy.
Jerry changed the cycle rate from 6 cph (10 minutes) to 3 cph (20 minutes) by multiplying the amp draw of the load by 1.2. What happened to the comfort is a result of changing the cycle rate.
Picture a sine wave. When you reduce the number of waves over the same period, the waves not only get longer, they also must range higher and lower. So the temperature swing that was less than 2 degrees when the cycles were 10 minutes expands to 4-5 degrees or more when the cycles are 20 minutes.
ApplicationsWhen you increase the number of cycles, the temperature swing gets smaller. At first that seems like a great idea, but the down side is that rapid cycling is hard on the equipment. And people often find the frequent on-off cycling to be annoying.
There are appropriate applications for both longer and shorter cycle rates. Three cycles per hour is a good setting for huge, old-fashioned cast-iron radiators. That's because they radiate heat for a long time. Fin-tube baseboard is a much lighter mass and is just fine at six cycles per hour.
Nine cycles per hour is good for electric strip heat because electric heat dissipates quickly. Nine cycles per hour is the amp draw of the load times a factor of .8.
What about in-floor radiant heating? The jury's still out about that. Here's something incorrect that I often hear: "Just push the anticipator all the way to the end. You don't want an anticipator in there anyway because that floor's a really big mass." Now that you know about anticipators, you, too, can probably see a couple problems with this. The anticipator is there to provide comfort. In-floor heating is about providing comfort, so we certainly wouldn't want to take the anticipator out, even if we could.
But setting the anticipator to the end of the dial doesn't take it out. Depending upon which end you choose, it either makes the cycles extremely short or extremely long.
Furthermore, that floor isn't always a big mass. What if it's hardwood? What if the tubing is staple-up -- under, not in, the floor? What if you've just started a long heat cycle and the Colorado sun starts beating into a two-story southern exposure window? Hoowee, that's a lot to think about.
I'm a fan of staying with the six cycles per hour for in-floor, to at least see how it does. The reason is because six is the industry standard for staying within a two-degree temperature swing, without cycling the equipment excessively. And six cycles per hour gives a chance for correction every 10 minutes.
Tell me what you think. I'll share good ideas in upcoming columns.