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# Using TRV's on steam cut down your EDR??

Member Posts: 268
radiators would cause an oversizing effect?

I know the TRV's prematurely cut the rad off so that it doesnt overheat the room, but would this be the same as if the radiator wasnt there?

Lets say you have 6 rads, 3 with the TRV's, now assume your boiler was properly installed for the proper sq ft EDR of your rads and pipes.

By cutting out 3 rads during the heating cycle ,doesnt that reduce the EDR for the whole system, causing your boiler to build pressure more quickly ,giving you the same results as an oversized system??

• Member Posts: 398

Yes, on paper I think you are correct. It should not be so critical that you have no room for adjustment. Are you building pressure Now? If so you may be oversized. Not a pro. but my system has lots of room for adjustment with no pressure problems (maybe too much) I hear nothing but good about the valves (other than the price). good luck
• Member Posts: 231
Probably right, but

Even so, unless the TRV usage is excessive, I'd guess you're ok. I'm not a pro, of course -- I just like to make stuff up. (There's the caveat for you.) Here's my reasoning:

Let's say you have 6 rads (all of equal size). If you put TRVs on 3 of them, I can only guess that's because they're too big. Let's say they're on average 33% biger than they need to be.

The TRVs will shut off, presumably, when the radiators are two-thirds-hot. However, since steam will still condense in that half, it'll create a partial vacuum and still draw in more steam, so it's not like the radiator shuts off, it's just like the radiator is 2/3rds as big.

Now, let's do some fuzzy math. Let's say each radiator is 30 sqft. 6 of them means you have 180 sq ft. Let's say you have a 1.5 pickup factor, so that's an extra 90 sq ft, so the properly sized boiler would have a DOE of 270 sq ft.

If you cut off 1/3rd of 3 of the radiators, then you have about 150 sq ft of radiators. But you'll still use the same pickup factor as before (90) since you're still going to have to heat the same pipes and so forth. So then your boiler would need to be about 240 sq ft. versus 270 sq ft., or a difference of 11-12% or so.

-Michael
• Member Posts: 268
well dont you build pressure

after all the rads are giving off heat?
• Member Posts: 16,728
Trouble is

on the coldest day of the year, you may really need to heat all the radiating surface. In this case an undersized boiler probably won't cut it.

Dave "Boilerpro" Bunnell has been experimenting with this however, so depending on what he finds it might become feasible.....

All Steamed Up, Inc.
Towson, MD, USA
Steam, Vapor & Hot-Water Heating Specialists
Oil & Gas Burner Service
Consulting
• Member Posts: 398

No I don't. But I believe that my system (100 years + and has been modifyed over the years) is still under sized. My goal for the trv is to make up for the uneven characteristics of my building. Windows outside walls no insolation etc. The weather is a very big factor in my situation. Would like to know more about the valves.
• Member Posts: 99
check the library

on Thermostatic Radiator Valves. Dan was kind enough to post a document that Danfoss made many years ago explaining the theory of 1PS systems.

The TRV stops the air from venting when the room temperature is satisfied, not when a percentage of the rad is filled with steam. So, on a colder day it will take longer to close off, while on the shoulder seasons they will close sooner as the heat loss is less.

Please remember that when installing 1PS valves that it is best to ensure that the many factors of the system such as: radiator pitch, supply valve is fully opened, proper boiler room piping with insulation, steam pressure is set to cut on @ 1/2 psi and out at less than 2 psi.

Warm Regards,

bb
• Member Posts: 2,542
What they WILL do...

I had situations very similar to your where some rooms were hotter than hell, and some rooms on the far ends of the system were cold.

We installed the TRV's and the temperatures balanced out immediately, AND the system actually built up pressure. In one case, the boiler was 50% under matching standing EDR. It made the problem all but disappear. When we first got there, the pressure on the top floor was neutral to negative. If you took the air vent off, the radiator was panting like a hot dog. Once we installed TRVs throughout, the radaitor has pressure and gives off heat.

The room is still somewhat cool, but thats due to exposre and a lack of thermostat in that room (top floor, outside corner). The HO has been instructed of how to "herd heat" up to that room when it gets extremely cold outside.

In my professinal opinion, EVERY one pipe steam system should have them. They keep people truly comfortable, AND save fuel money.

As for cutting down on EDR, they don't cut it down, but they do limit its exposure to the boiler, but from the standpoint of pick up, I think the total EDR SHOULD be matched at a minimum.

I'm not sure that the 50% pick up factor is as critical, but matching the EDR to the standing load is important.

I suppose as an experiment, as long as the EDR exceeded the actual heat loss, the boiler could be sized to the heat loss instead of the EDR requirements, and with the use of TRV's the loads would be shifted to those areas actually experiencing the loads. I wouldn't consider doing this in my customers homes, but if I had a 1 pipe system in my own home, I'd consider it, based on the fact that I applied it in the situaion where the boiler was half as big as it should have been...and it worked like a CHAMP.

ME
• Member Posts: 231
library

Say, this is pretty cool. And I thought I had already read all of the good stuff there. . .

Anyway, the "% of radiator getting hot" idea I think stems from a typical winter day where radiator is oversized due to changes in the home (smaller room due to moving walls, adding insulation, window improvement). Since the EDR of the radiator would exceed the heat loss, one could roughly translate the point at which the room came to temperature to a certain amount of the radiator being heated. Of course, this percentage would vary depending on the actual temperature outside.

-Michael
• Member Posts: 231
on the flip side

On a similar vein, I have to wonder: if the pipes and pitch were large/steep enough to handle the increased condensate, could I compensate for an oversized boiler (and help quell my general impatience) by attaching fans to the bottom of my radiators?

-Michael
• Member Posts: 398

Am I wrong, or shouldn't a radiator with proper designed size be only partaly heated on any day less than the coldest design day? Excellent info in the TRV thanks. Any brands you have good experiance with?
• Member Posts: 231
radiators will heat all the way across

quite often, even if it's not a design day. Let's say you have a room with a heat loss of 4800 BTU (to make the math easy). This sizes out to a 20 sqft radiator.

This means the room loses 4800 BTU on the design day if it's 65 degrees inside (or 70, or whatever you calculate your heat loss to) and the design temperature outside. If it's colder on the inside or warmer on the outside, the heat loss is lower.

Let's say, for example, your design temperature assumes a 70 degree difference between inside and outside (70 degrees inside and 0 outside, for example). If it's 10 degrees on the outside, your heat loss will be lower than 4800 BTU. To make the math easy, let's just say for the heck of it that you would lose 4360 BTU at this outside temperature when the inside is 70 degrees.

Theoretically, then, you need only 18 sqft of your 20 sqft radiator. If you could lop off 2 sqft and then let it sit there fully hot, it would succeed in heating the room to 70 degrees. While the room is, say, 68 degrees, the heat differential smaller so the heat loss would be just under 4360 BTU. So the 4360 BTU given off by the radiator raises the room temperature. This proceeds until the room temperature reaches 70, making the heat loss in the room 4360, matching the radiator.

Of course, the radiator doesn't know this is going to happen, and you're impatient, so the radiator heats all the way across because it takes less time to heat the rest of the radiator than it takes for the room to slowly come to temperature. So the radiator heats all the way and starts spitting out 4800 BTU, which means that if it stays fully hot, it will continue to heat the room even after it reaches 70 degrees, because at that point the heat loss is still only 4360 BTU. This results in overshooting the thermostat and the use of anticipators and so forth. On a design day, with a radiator matched exactly to the heat loss, I don't believe you'd ever overshoot the thermostat; instead, you'd just asymptotically come to temperature.

Radiators don't heat all the way across if the heat loss is so low that the thermostat is satisfied before the radiator is done heating -- that is, the room temperature rises quite quickly.

Anyway, that's just my understanding. The level of detail I've given, of course, impinges on the garbage-in, garbage-out level of specificity, I think. But heck, it's fun.

-Michael
• Member Posts: 141
no no no i think

The boiler's pick up factor is not reduced. If you undersize the boiler, it is undersized. The piping is all still there, and the TRVs are open when the system starts. So everything will take too long to heat until the TRVs start to close. Now the boiler is running excessively long to deal with the pick-up load. Your efficiency is down the drain.

Size the boiler properly for the piping and EDR. Set the pressuretrol as low as it will go, continue to use the TRVs, and be happy.

BTW, if you think yanking those rads is going to save you a bundle, see dan's books on boiler sizing. You have to count the radiators that are missing, too. Or at least a portion thereof because the main and risers are sized to supply that EDR whether the rad is there or not.

My two cents.
• Member Posts: 398

Mark, Who makes a good TRV? These are for apartment use.
• Member Posts: 2,542
Danfoss RA2000 1PS

It comes with the possibility of numerous varied and differing operators. They also have a 24 hour programmable set back capability for their stack on units. Best there is. You'll also need new angle vents to work with these.

ME
• Member Posts: 60
vents

Thanks for the kind words Mark, but the vent needs to be a straight one, for the Danfoss 1 PS valve to work, the vent needs to be at 12 o'clock and the vaccumn breaker at 6.
DWood
• Member Posts: 99
it's amazing

what you can find in the library.

Thanks Mr. Holohan for sharing the knowledge!

bb
• Member Posts: 272
one pipe trv's

lets not forget the macon OPSK one pipe steam valve. look up their web site wwww.maconcontrols.com good stuff
• Member Posts: 2,595

• Member Posts: 2,542
DOH!!

Thanks Dennis, My mind knew what I was trying to say, but forgot to communicate it correctly to my fingers...

You have to get rid of the ANGLE vent and replace it with a STRAIGHT, because the TRV body plugs in where the angle vent USED to be...

ME
• Member Posts: 398

For us dumb guys is the angle vent the regular old steam/ air vent that is on the rad. now? Have a 1 pipe steam sys.
• Member Posts: 2,542
Yes...

That's correct.

ME
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