Convector vs. Radiator in Custom Cabinet Enclosure

superMARKet

I’m replacing some convectors in an apartment. The building has a two-pipe steam system.

Right now, I’ve got some copper-tube aluminum-fin convectors (60, 60, 50, and 30 square feet EDR). These are going away.

The existing convector elements are hiding out inside some millwork with grilles for airflow. I asked an engineer to specify some cast-iron replacements. I expected them to specify cast-iron convectors. Instead, they came back with cast-iron tube-style radiators (Gov-Free) and down-sized everything (24, 30, 18, and 24 square feet EDR).

I know that these radiators will convect just fine if that’s what I ask them to do, but is it appropriate to stick them inside an enclosure? I found this article by Dan and Steamhead. My enclosures most closely resemble the top right (“deduct 5%”). Should I go with this, or would there be a benefit to using a shorter (in height) but longer (along the wall) convector element?

KC_Jones

Couple things come to mind
1. Are you replacing everything in the system, or just part of the system?
2. What is the heat loss of the spaces those radiators are specified for? Those number should be available as it's the only way to size.
3. If you are only replacing part then the emitters would need to maintain balance or have some way to adjust output. For example if your current setup is 25% over sized for the heat load and you replace with emitters that are exactly to the heat load then you potentially mess up the balance in the apartment as a whole. The new emitters IMHO should be sized similar to how the originals were sized.
4. The free standing cast iron will perform differently from the convectors. The convectors will tend to heat when the steam is on and quickly stop heating after it shuts off. The cast iron will tend to radiate for a long time after the steam shuts off. Again this ties in with system balance.

Is the person you are working with a steam expert? Steam has a lot of subtleties to it that must be addressed.

superMARKet

Thanks, KC!

1. This is one apartment in a large building. I’m only replacing these four convectors. Everything else stays the same.
2. I’ve been trying to get the engineer to share heat load calculations, which they haven’t done yet. (Same problem for cooling, actually.) I don’t want to assume that they’re just eyeballing it, but…
3. I’ll have thermostatic control over the new convectors or radiators. I know I can’t make the burner fire, but I can at least modulate what it provides.

KC_Jones

superMARKet said:

Thanks, KC!

1. This is one apartment in a large building. I’m only replacing these four convectors. Everything else stays the same.
2. I’ve been trying to get the engineer to share heat load calculations, which they haven’t done yet. (Same problem for cooling, actually.) I don’t want to assume that they’re just eyeballing it, but…
3. I’ll have thermostatic control over the new convectors or radiators. I know I can’t make the burner fire, but I can at least modulate what it provides.

What I mean about replacement is, are you replacing everything in your unit or only part of your unit.

The TRV's will only stop overheating, so be aware of unintended consequences. Also if the control of the system isn't proper, they won't work at all.

The pressure must be kept low, and the system must cycle otherwise they won't work or won't work well.

If they are doing proper calculations, are in contact with building management for the control set up, you should have zero need for TRV's.

superMARKet

Yes, replacing everything in my unit.

They’re not TRVs, they’re zone valves.

KC_Jones

superMARKet said:

Yes, replacing everything in my unit.

They’re not TRVs, they’re zone valves.

Make sure they are piped correctly, zone valves can be a real problem on steam if not done correctly.

https://heatinghelp.com/systems-help-center/zoning-steam-systems/

superMARKet

Thanks, KC! I already worked that out with you nice people and the conclusion was what I’m doing shouldn’t be a problem for such a small chunk of the overall system.