Optimal Heat Transfer from Radiators

Fred Harwood_2

Are you measuring the actual radiator, or the exit air temperature from a convector?

Property Manager

I have a question for you experts. This is for a 2 pipe steam system in a 30k sq ft commercial building.

Question #1
If some radiators only get to 150 degrees while other radiators in other parts of a building get to 230 degrees, what does it mean? Is the PSI not set high enough?

Question #2
Some radiators are giving off 220 degrees of heat. But, when I stand next to some of them, it's very hot. But, standing next to others, it's not very hot even though these also show that it's 220 degrees too. Is it possible that the paint or the dirtiness of the radiators affect the amount of heat transfer?

nicholas bonham-carter

au contraire

if you have really measured a radiator surface temperature of 220 deg, the pressure would be set too high. i think that the surface temperature should be no more than about 215 deg at each rad, and ALL EQUAL [sounds like some of yours are more equal than others].

use the melting butter test with a helper to establish whether they all get equally hot at the same time.

get a copy of dan's "the lost art of steam heating here and look at the chapter dealing with 2-pipe systems. i think the steam arrival at different rads is varying too much, possibly due to venting problems coupled with high pressure[some 2-pipe sytems work at 2 ounces!]--nbc

Property Manager

Sorry. The radiator temp is probably 215. i was only writing down an approximation.

Problem #1
Some radiators in the system only reach 115-130 degrees. And, they never get warmer. I read holden's book about 2 times. I dont have any vents in this system since I have a condensate pump which I assume is acting as the vent to the system.

Problem #2
Any ideas on why 2 different radiators that show 200 degrees but show differing amounts of radiation when I stand next to them?

Property Manager

I'm using a laser thermometer on the actual radiator.

Do you think cleaning the surface of the radiator will make a difference?

Jamie Hall

Fun, isn't it?

Property managing, that is.

You absolutely have to have vents. The condensate return is just for that; it is not meant to be, and won't work as, a way to get air out of the system which you have to do to allow steam in. If you have good cross-over traps at the ends of the mains, then what you need is a good big set of vents where the dry returns drop to the wet return or pump. On the other hand, if you just have drips at the ends of the mains to the wet return, then you absolutely need good big vents there, too. Doing that will solve much of the problem of the low temperature radiators.

I have found that in my building, the apparent heat from a radiator can vary a lot because of differences in air circulation; a better test is to feel the temperature and amount of air rising off the radiator. Much more reliable. Although a metallic painted radiator won't radiate anywhere near as well as a regular painted 9or unpainted) one will.

Do keep the pressure down. Raising it will accomplish nothing except raise your fuel bill.

Property Manager

Property managing is fun. And, thanks for your help. It's great.

I was assuming the air vent in the condensate pump was sufficient but I guess you are saying that it's not sufficient. I guess I need to install some big vents in that area of the building. I'll consult with Clammy.

With respect to testing radiators, are you saying that I should go by the feel of my hand rather than my laser thermometer to see if steam is reaching the radiator sufficiently?

rob brown

if those rads are painted with reflective paint you wont get an accurate temp reading with an infrared thermometer.(the laser is just to help with pointing). bare copper pipe has the same issue, and it's due to the emissivity of the material being checked.either use an old fashioned contact type thermometer or paint a small flat black spot on the rads to shoot your temps. i've also used a piece of masking tape to cover the reflective surface. not recommended for steam tho. rob

nicholas bonham-carter

butter

for checking the speed of steam arrival, melting butter never lies! just make sure the butter pats, and plates are all the same size, and temp when you start. all the butter should go liquid at the same time. don't worry about the temp for now, it's the steam arrival time you are most concerned with here.

don't forget the toast to have when you are finished!--nbc