Not Enough Radiation?

Javelin

Heating Pros,



With a ton of help from this forum and expert advice I'm the proud owner of a new Triangle Tube Prestige Solo 250 boiler. It's new this VERY cold season, let's us afford to keep the house at 67 instead of last year's 60, and is still much cheaper to run even with the new indirect nearly endless DHW tank. Love it.



That's being said, the house is big and old.. about 5,600 sq/ft, minimal insulation, etc. I've been replacing windows this past year, and new insulation wherever I can. The house has two zones... One zone is the entire house, and the 2nd zone is an add on room that used to once be an exterior porch.



While most of the house has free standing cast iron radiators, the one addition room has these convector? radiators positioned in built in cabinets under the windows. The problem is that even on very cold days (which we've had this winter) - the TT boiler with it's outdoor sensor is properly pumping out it's max 192 deg. water sometimes, but even when it is, this room isn't getting up to temperature. Will only get up to about 63.



Now I plan on eventually ripping open the ceiling and will add insulation then, and we're also getting the crawlspace below encapsulated which I'm told COULD help retain some temps..



My questions to this forum.. it doesn't seem like these convector rads are producing anywhere NEAR the amount of heat that the radiators in the rest of the house are producing. Is this normal? Even the return pipes in the basement from this zone are still wicked hot (whereas the rest of the house zone "dumps" a lot of its heat quite obviously) Is there a way to increase radiation on these convector rads? Should I try to replace these old convectors with more traditional stand-alone cast iron ones from a company like Governale?



Thank you so much in advance for any suggestions/input/direction.



Please see two attached photos.. One a mockup of one of the walls where the radiators exist (3 walls total), and the other a "top-down" view of one of the radiators.



Jay

unclejohn

Load calc.

Thats the first step.

SWEI

Are the pipes to the convectors insulated?

What were the room temps like with the old boiler, as compared with other rooms in the house?

Javelin

Unknown Temps...

SWEI, we had a VERY inefficient old boiler in the house and we kept the entire house (and this 2nd zone room) cold. In generally though, that one room always seems to be colder than the rest of the house by a few degrees... It seems to me that it's making about 70% of the required temperature, then that room is borrowing another 15% from adjacent rooms (from the heat generated from the normal free-standing CI rads), then coming up short the other 15%.



Obviously that's not a very accurate or scientific response, but maybe a rough idea?



One thing of note.. this one big room which is roughly 16' x 36' has these radiators under each of the 4 window areas, but that room/zone is being fed with a 1.9" O.D. iron pipe. The Bumblebee pump on that zone always seems to be going, but not too fast... Right now the pump is set to delta-T mode with sensors on the supply and return... would it possibly make sense to run it on another mode somehow? Just thinking... but obviously not my field.



Thanks!

Mark Eatherton

Differences….

First off, based on the photograph, your convector has no outlet. In order for a convector to work correctly, there has to be a place for cold air to get in, roll past the heating element, get hotter and lighter, and rise up to the convectors air outlet, where the heated air enters the room. This is the reason your S&R pipes are so blazing hot. The convectors are not releasing the energy contained in the water into the air. Need to cut some vents into the wall cavity to let the hot air into the room.



The other big difference is that in the rooms with the free standing radiators, you are dealing with 60% radiant energy, which manipulates the Mean Radiant Temperature. That is the temperature that you can't see (surface temperatures surrounding your body) but your body CAN sense a BIG difference. Even if the convectored room were able to achieve an air temperature of 70 F, and the radiated room was also at 70 F, when you walk between the two rooms, your body IS going to feel the difference. Not much you can do about that scenario, other than posting sweaters at the entry way into the convected rooms :-).



Once you get the air side of the convectors freed up, the hydronics should follow suit, and the room should warm up.



BTW, most convector systems were DESIGNED for a 20 degree water temperature differential, but the real world norm is more like 7 to 10 degree differential. Set you Bee for 20 degree differential or less for that loop, and that should be just fine. Turning it too high will cause the water to slow way down, seriously affecting (negatively) the ability of the convectors to convey heat from the water to the air.







ME

Gordan

Outlet at the top

Not super-easy to see, but the outlet grill is recessed into the window sill.

Javelin

Thanks...

Thanks Mark - Gordan is correct, there are vents at the top of the built-ins, and also maybe a 3-4" high INTAKE along the floor below each convector, so I think the airflow SHOULD be ok... I'll look up how to adjust the pump for that differential and see how it works out.



Thanks a lot!



Jay

Gordan

Measure the temps

Measure the entering/leaving water temperatures at all the convectors, and in the basement at the zone supply and return. This should tell you where heat is actually being dissipated.



You could be hamstringing your convectors by giving them too little flow. What gpm is the Bumblebee saying it's providing to the zone?



If the emitters are simply undersized for this room (was this a converted steam system, for instance?) a supplementary emitter may be required.

Gordan

Regarding the outlet at the top

I can see pros and cons to that layout, but (I think) mostly cons: the convective current could be impeded by falling cold air from the window and whatever warm air makes it out could be getting chilled as it washes the cold glass. A pro would be that I'd expect less window condensation. An outlet facing the room seems like it would have fewer cons.



If increasing the water flow to your emitters doesn't fix your issue, one way to perhaps increase the effectiveness of the convector is to "assist" natural convection mechanically. You wouldn't benefit from very much assistance, looking at that convector (large air passages) but it could put you into the comfort zone with the high supply temps you are using.

Javelin

Cutouts...

Thanks Gordan... so eventually I'm planning on reworking this room... you're saying that I would probably benefit from cutting out new outlets FACING the room and covering over the old ones that face the ceiling? The air around those windows definitely is cold (even tight the new double panes I put in) - so I suspect that your thought is correct with some of that cold air hampering the output of heat into the room.



You said mechanical assistance... you mean some sort of fan that would turn on to move more air over the convectors?

Gordan

Yes, some sort of fan.

Let me tell you what I did for a particularly difficult room. This room has cathedral ceilings, a small floor area, and three out of four walls are exterior. It had been heated by one five foot and one 3.5 foot convector recessed in the wall like yours (but with the outlet facing the room.) The rest of my house, which I had converted to radiant ceilings (so: a low-temperature system) had been heated in the same way. I used the convector elements that I had ripped out from the other rooms and built triple-pass, counter-flow convectors for this room, then I covered the back of the grill with 1/4" plywood that had cutouts for the computer case fans. I used two 5" fans for the smaller convector and four for the larger. I picked fans of the quiet, low-CFM variety and I'm driving them with 6V even though they're 12V fans.  In my case, the desire to use low temperature water was what made the triple-pass approach necessary, and the fans are just there to overcome the greater air pressure drop across the elements and the lower temperature gradient of the air; they're not really "blowing" as much as "circulating." It has worked very well for me. On the other hand, I recall another member not having as much success with his attempt to just increase air movement over a single-pass, low fin count convector.

Javelin

ok.. thanks...

Gordan, Thanks again.. Will keep your thoughts in mind and try something, though admittedly, any major attempts will probably have to wait a while until I "get" to that room. I looked at the bumblebee on that zone and I think it was set to 25... I changed it to 12.. We'll see what that does... Honestly, I'm not really sure what that means.. I know it's related to the difference in temp between the supply and return line, but I'm guessing a lower value will make the pumps pump faster?



Thanks, again!

Gordan

Yes

The lower temperature differential means that, with a fixed supply water temperature, the return water temperature increases, meaning that the average temperature of the emitter (and therefore the amount of heat it can emit) increases for any given entering air temperature. In order for this to happen (increased return water temperature WITH increased heat loss from water to air) the circulator has to provide a greater flow of water.

Mark Eatherton

Got it...

Blind in one, can't see out the other …:-)



I was looking at the face of the wall and not the top of the deck enclosure.



Unless the air flow is perfectly ducted to these outlet ports, the resistance to natural convective air flow may still be impeding the transfer of heat. Without a remote snake camera, we may never know whats on the inside.



Generally speaking, the higher the stack effect, the great the movement of air, provided the enclosure is conducive to easy air flow. Hence why commercial baseboards are so tall.



ME

icesailor

convectors:

I can't tell if that is just a cast iron radiator cover or a cover made for a convector coil.

If it is the later, someone may not have understand how convector radiators work. Baseboards or cabinet types. The elements MUST be held tightly in the cabinet so that the cold air is forced to go THROUGH the elements and not AROUND the elements. When the air goes around the elements, the efficiency drops because so much less goes through the element. Unless you line and insulate the inside of the built-in cabinet space, the heat will be absorbed by the surrounding surface material.

A year or more, I was given a chart that showed how much decrease in BTU's there was from installing Cast Iron Radiators in a box cover. It was substantial, no matter how you designed it. 20% to 50%.



If you look at box convector outlet ratings, they always give outlet air temperature. If the rating for a convector that you chose (as an example) rated the unit with say 130 degree outlet air, and it is only 110 degrees, there is either a lot of air leaving and not being compressed, or the air is bypassing the coil element and not heating up.

I once had a job where the owner didn't want to look at baseboard but wanted the elements enclosed. He had some expert carpenter/builder tell him that all he needed was the one element of #80 slant fin. I put 6 rows in and it worked fine. Just barely though. At too was on its own zone.

If you can take that apart and add a few more elements, you'll get more heat out of it. Because it is already a zone, it won't matter HOW MUCH heat you put in there.

RobG

Orientation

How are the convectors mounted? I cannot tell from the picture. Is the picture from the top, looking down, from the bottom looking up or from the side? They should be mounted horizontally so that the air is pulled in from the bottom, goes through the fins and exits at the top. The picture looks like it is mounted vertically

Javelin

I think it's proper...

RobG, The photo above was taken from ABOVE.. I removed the metal "screen" on the cabinet below the window and took a picture inside. It looks like it's installed properly to pull from the bottom and go through the convector, then out the top..

EBEBRATT-Ed

probably a combination of

not enough, radiation, insulation etc. Also Ice has a point about the space between the convector and the inside walls of the enclosure it looks like their may be to much space. the enclosures should be insulated and metal lined.

having the opening on top is better for the stack effect than in the front. is the return air inlet far enough below the convector inlet?

Also the enclosure grills (expanded metal) try removing them inlet and outlet and see if it improves the heat. They may have openings that are too small.

Gordan

There's no doubt

Clearly a straight upward shot (and the little bit of added height) would be better for convection if the convector were sitting in the middle of the room, away from any windows or exterior walls that could create downward cold air currents. But it's not sitting in the middle of the room. We're guessing here, anyway - the way to see what's happening would be to place a piece of incense on the outlet and watch what happens with the smoke. Then a cardboard deflector could be temporarily taped in place at a 45 degree angle, angling up and away from the corner between window and back of window sill, and the test could be repeated.



The grill he has appears to be of the "grid" variety, not an expanded metal one. I doubt it's creating any impediment. There's no grill on the intake.

Paul48

At Best

The output of those elements will be similar to those of standard baseboards. You need to do a heat loss for the room. Try as you may, "you can't make a silk purse out of a sows ear". 

icesailor

Old Dead Wetheads:

Old dead wet heads always placed radiators or convectors in front of windows. As a thermal barrier.

Its not wrong that it is located there, its just restricted too muck as built. Place some poly foam board insulation between the walls and the element coil. Put one full length from the floor to the bottom of the cabinet to stop heat loss to the outside, and it will improve. After you cot holes in the bottom of the wall for the colder air from the floor to enter. Drive all the air you can through the element.

If I was confronted with that situation and had no other easy options, I would get the plugs out of the top of the CI units and put a copper fin tube element from Beacon Morris convectors and add to it. The IDEA of OK. The application needs improvement.

Gordan

Oh lawd, please don't let me be misunderstood

I'm not suggesting that it should be in the middle of the room, just that the falling air film from the window might be fighting the convection currents since they're coming right at each other. :-)



The side-discharge that my convectors have seems to create a warm air barrier without mixing excessively with the cold window air. It would be interesting to thermographically compare the two setups, holding all else equal.

Paul48

Porch Conversion

The thickness of the wall in the photo, suggests they may have built walls within walls. I read a posting here( to which someone from Burnham was responding) that stated that just stacking convectors produced little difference in output, because it just created interference to convective air flow. The addition of the fans would counteract that though. I don't know how you would calculate the output of the modified emitter, other than trial and error. Without a proper heat loss,there is no way of knowing whether you could get close to correct by just increasing the output of the existing enclosures.

ChicagoCooperator

Careful if moving the register location

You lose a bit of convective effect by shortening the "chimney" of the convector (in some applications anyway - i.e. Trane Concealed Heaters, etc). Make sure the window is reasonably weatherstripped and the convector element is clean (and the intake and register aren't blocked - which I'm sure you've done).