Thermostatic Radiator Valves
Although it was just past three o'clock in the afternoon, it was almost dark when we checked into our hotel in Stockholm. Snow was falling, but not heavily enough to slow the work of the men who were installing the hydronic snow melt system under the cobblestone sidewalk down the street. Sweden, I quickly learned, is a Wet Head's paradise.
I threw my suitcase on the bed and walked toward the radiator. The room suffered from Eurochill (You're cold? Put on a sweater!). The radiator, of course, was hydronic. Most of the radiators in Europe are hydronic. This one had a thermostatic radiator valve attached to a steel supply line that was the Metric equivalent of about 3/8". Most of the heating professionals I know in America would bet money that you couldn't possibly heat a hotel room with a pipe that puny. But there we were.
My hotel room, like so many rooms in Europe, had the heating pipes mounted on the outside of the wall. I once asked a European engineer why they install their pipes in such a visible way. "Vee do it dis vay," he explained, "so dat shud dey break, vee can fix dem qvick."
In Europe, the stupidity of my questions often stands out like a splattered bug on the windshield of a new BMW.
Anyway, my room was as cold as a stainless steel flagpole in January, so I grabbed the TRV's actuator and gave it a manly twist. It spun right up to its limit and stopped, but I didn't hear any water flowing into the panel radiator. Hmmm.
I waited a minute. Then I whipped out my Swiss Army knife, unscrewed the actuator from its valve body, popped it off, and recalibrated it to about 80 degrees Fahrenheit. I did this because I knew how to do this. And because I could.
Thermostatic radiator valves, or TRVs for short, have been around for a long time. The Empire State building, built in 1929, had them. They ran on steam back then, and they still do today.
TRVs last a long time because they're so simple in design. You start with a normally open, spring-loaded valve. Next, you take a bellows that's filled with a chemical that's very sensitive to air temperature. Then you enclose the bellows in a tough plastic shell, which you'll twist to adjust the tension on the bellows and change the temperature setting (we'll call this part the "operator"). Finally, you'll mount the operator on the spring-loaded valve and that's a TRV.
The TRV's bellows usually has a thin, metal sensor that sits out in the air like a mouse's tail and senses the room-air temperature. Installers, who are often handymen or building superintendents, will think nothing of mounting these crucial, room-air-temperature sensors, right on top of the radiator element. This, of course, leads to very memorable, building-wide "No Heat" calls.
Handymen and building superintendents will actually jam the TRV sensors between the fins of the heating elements. How come? To hold them in place! These people are wildly enthusiastic about what they do. Some use Krazy Glue.
They will also jam a TRV's sensor under a rug or a flap of linoleum. That keeps the sensor safe - and clean. Some handymen and superintendents mount the sensors on the radiator's supply pipe. That keeps them stable. They will also place the sensors precisely along that uncaulked crack between the floor and the wall. The low-bid building contractor left that crack as his legacy. This crack is the place where, in most older apartment buildings, Mr. Breezy slips in whenever the exhaust fans starts. No heat! Hmmm, I wonder why.
I remember troubleshooting a frigid New York City high-rise once. They had steam heat and, at first, everything looked fine. The contractor had mounted the sensors on the wall, right next to the recessed steam convectors. It was a textbook installation. The sensors should have been feeling room-air temperature and the comfort level should have been perfect, but it was much too hot in this place. And the worst part was, the TRVs were closed!
It took us a while to figure out that behind the wall the contractor had chosen for his sensors stood the chase for the uninsulated steam risers. Hot stuff! Even when we relocated the sensors, this place overheated. The TRVs were shut as tight as new pickle jars, but the rooms held steady at 80 degrees Fahrenheit. It was a real lesson in Mean Radiant Temperature.
How did the folks solve this problem? They did what folks in so many New York City apartment buildings do. They opened the windows. The Ol' Double-Hung Zone Valve does the trick every time.
But enough about handymen and superintendents. Even professional heating contractors make mistakes when they snap those operators onto the valve bodies. You see you have to position them just so, and that's often tough when you're twisted like a yogi under the radiator and the sweat's running into your eyes. If you tilt the operator too much, the valve body's stem won't align with the part of the operator that's designed to receive it. They slip by each other, and from your position on the floor, you can't tell that the marriage wasn't consummated. You wind up with a valve body that's forever open. But everything looks fine from where you're lying on the floor. The room goes to 90 degrees, and everyone gets mad at the TRV manufacturers. But it's not their fault.
And while you're troubleshooting, don't forget that engineers, too, are only human. I once looked at a problem job on Long Island where an engineer had specified TRVs for a perimeter loop in an office building. This guy called for 1-1/2-inch, commercial, fin-tube baseboard and a TRV in every office. Trouble was, he didn't specify bypass lines from one office to the next. Only the woman in the first office was comfortable; everyone else froze. Talk about the power of a corner office!
And then there was that memorable day when the contractor installed about 700 TRVs in this hot-water-heated, Manhattan co-op. The engineer told the shareholders the TRVs would balance the temperature and improve their level of comfort significantly.
The contractor started the job and the valves went to work. As the rooms got warm, the TRVs closed, and in closing, they shoved the base-mounted pump back on its performance curve. The pump built pressure as it crawled up that curve. It didn't take long for all that pent-up power to shove the "closed" valves wide open. Seven hundred, brand-new TRVs and the building was overheating.
It hadn't occurred to the engineer to check to see if his new TRVs were going to be compatible with the old pump. As time went by, we all came to appreciate flat, 1750-RPM pump curves and properly sized pumps. You live and you learn - and you trim many pump impellers along the way.
On one-pipe-steam, I learned that TRVs don't work well with angle-pattern steam vents. You're not controlling the steam on these jobs; you're controlling the release of air from the radiators. The TRV goes between the vent and the radiator, and since the radiator starts with an angle-pattern vent, it's tempting to use the same type of vent with the TRV. Trouble is, the condensate won't drain from the angle-pattern vent. You have to use a straight-pattern vent instead.
I also learned that TRVs for one-pipe steam need vacuum breakers to work properly. The steam pushes the air through the TRV and out the vent. The room comes up to temperature, and the TRV closes. At this point, no more air can escape from the vent. The steam condenses and leaves a partial vacuum in its place. Since the TRV is closed, air can't get back into the radiator through the air vent. The partial vacuum in the radiator sucks steam from the mains and risers, and the room overheats. It took a while for TRV manufacturers to figure this one out.
I've also learned that TRVs can't solve distribution problems in old steam systems. All they can do is keep radiators from overheating. Many people think that if you stop the steam from going into one radiator, it will automatically go to another. Unfortunately, it doesn't work that way with steam. Distribution depends more on pipe sizing and configuration, the boiler load, air venting, pipe insulation, water quality, steam traps, the vacuum pump, and, the building superintendent
Be nice to that building superintendent.