Increasing output with a semi-cover

Jakek

A few weeks ago I enjoyed the write-up Dan and others posted on radiator covers and have been thinking about it ever since. From the diagram, one can make an otherwise uncovered radiator more efficient by adding a solid board 2" in front of the radiator with space for airflow at the bottom in order to create a chimney effect. That seems like a pretty cheap improvement and can even look nice if done artfully.

Has anyone made this change and found the room feeling warmer as a result, all other things being equal?

As a related question, is there any downside to cooling a steam radiator quickly, as would be the case with a passive method (above) or a active method such as a fan? In an extreme it seems like it would unbalance the system and possibly waste heating fuel.

And perhaps another topic entirely, from a fuel conservation standpoint is it better to bring a radiator to peak temp (pressure cut-off), kill the fire, and let it "coast" for a while (15-60 min) before restarting the process or hold the temp at a high level until the set-point is reached? It would seem the former is preferable if the occupants are OK with slow heating.

Jamie Hall

Can of worms there... on cooling a radiator (either passive or active) -- no, no downside at all, at least to the radiator. There might be a balance problem, but unless you really got aggressive it should be minor.

On control... there have been many discussions on the Wall regarding control -- one just recently sort of wrapped itself up (I hope). There are differences of opinion... the question you ask, though, is on fuel economy, and there have been very few if any decently controlled studies on this. My own feeling -- and others differ -- is that if it is necessary to cycle the boiler at all (hopefully, if the system as a whole is properly matched it won't be) pressure is the better control -- provided it is set correctly which usually means on the order of a few ounces to half a pound for the cutout. Others feel that some form of timer arrangement is better. In any event, what you don't want to do is to let the boiler cool significantly between on phases. The other thing you don't want to do is to let the system run until you reach the setpoint temperature, as that will cause significant overshoot in the space temperature which is both uncomfortable and undesirable. As @PMJ said in that other recent thread, it's all about control strategy.

Jakek

Thanks @Jamie Hall. Last winter I connected my vaporstat to a database so I log every time the t-stat calls for heat as well as the times when it reaches and releases on pressure (4oz). I also log the outside air temp and room temps. I'll share my findings with the Wall once I have a few months of reading. One of the questions I hope to answer is if it's better to wait until the full 4oz is reached or to monitor the temp of the far side of a radiator and kill the fire when it gets hot. The system is well balanced.

But that brings me back to figuring out how best to optimize radiators. My goal is to save fuel (nat gas) while having the space moderately comfortable. We're more tolerant of temperature swings than others.

AMservices

I see a lot of radiators in my travels. One feature I see (usually more in recessed wall radiators and wall converters) are air dampers built into the cabinet design.
If you want to play with cabinet design, then I would suggest starting way over sized. Build it so you can easily adjust the openings on top and bottom, giving you control over the chimney effect.
Keep track of room temperature and see if you can raise it faster with different size openings.

acwagner

@Jakek I did something similar to what you are doing, but instead of logging the vaporstat status I logged the burner valve state. I originally did this to see if temperature setback had any impact on fuel consumption.

A point to consider is that you have to keep a very detailed log of the weather that includes solar gain and wind. Outside temperature is not the only factor, and it makes a indepth comparison between "similar" days very difficult unless the weather in your area is almost nearly constant from day to day.