Is there a "best" way to balance ductwork? Now that summer has hit, I have one large "sun room" (lots of windows, skylights) that is probably 10F warmer than rest of house. It is supplied with a large trunk and 4 8" ducts in the 4 corners, plus 2 good-sized returns, but it still heats up like you wouldn't believe. There is solar film on the windows & skylights. I've read that I could reduce all the cooler rooms by 1/3 using the in-line duct dampers then see how the temp adjusts over a few days. Is this current thinking, and if not, can someone direct me elsewhere? There is just an open doorway between this room and the rest of the house, but the vaulted ceiling seems to trap and concentrate the heat, even with the ceiling fan on. I'm seriously considering making it a 3rd zone since it is supplied by its own trunk that could be dampered.

Yes, you would partially restrict airflow to the cooler rooms to achieve balance. That might mean closing dampers 1/3, 1/4, 1/2 etc. Just be sensitive to the remaining opening (make sure we have enough airflow for tonnage of system).

Joe's right.

What a bummer of a room.

Is there anything you can do to add shade OUTSIDE the offending glass?

Posted By decafdrinker on 29 May 2012 02:09 PM
Is there a "best" way to balance ductwork? Now that summer has hit, I have one large "sun room" (lots of windows, skylights) that is probably 10F warmer than rest of house.

I bet if you closed the doors to that sun room the temps would be A LOT higher than just 10F. More like 20-30 degrees hotter. The room is bleeding off that heat gain to the rest of the home but if you secluded that room off, it would become an oven.

As you already know, what you are experiencing is solar gain overheating. Where are you located at? What is the SHGC of these windows?

The best solution would be to STOP the SHG BEFORE it gets into the room. That means shading the windows on the OUTSIDE. Not an easy thing to do.

Not sure all the specs of the room, basically it's about 22x22 with a vaulted ceiling about 15 feet at the peak with a ceiling fan. One wall is part of the house, so just a doorway (double-width). The remaining 3 walls have between 4 or 6 Caradco Casement windows on each wall ( from 1991 (not sure the rating)) Windows are maybe 16x48 each. Only one wall of 6 windows faces south, and then one of the faces of the slanted roof (2 skylights) directly faces the sun. I know window film was installed, I'm just not sure where (I have a receipt from the previous owners, but it doesn't say which exact windows, and I can't tell from looking at them). Walls appear to be standard 2x4 with 1/2 drywall inside and plywood/wrap/vinyl siding outside. Roof is 2x8s.

I hate to cover them because the view is spectacular! Could I get/build some sort of EXTERNAL skylight shade? Maybe like a mini-exterior rack of angled slats that in winter would allow light but in summer with the sun higher would cast shadow?

I understand blocking the sun BEFORE it gets to the house would be ideal. Trees will take far too long, though. Decades!

Maybe trellises with vines in front of the south side of the house, and something fancy on the skylights to cast shade?

.......or attack the load. Great place for a minisplit.

Where is it located, Stuart?

Have you poked around to see if the ceiling is properly insulated or not?

How high up towards the peak are the skylights? It might be worth it to replace one of them with a quality motorized opening skylight. That would get you "stack effect" venting for that room during periods of heat load.

You can get sunscreens for the exterior that are somewhat see through. That way, the view isn't totally lost.

Assuming that the heat load is coming from the windows and not from inadequate roof insulation or poor skylights, you might try extending the eaves of your roof (like your rack of slats idea) over the windows to get better shading that way. People have even put on shades using PV panels.

3rd zone! Can you add another zone without a new control board? If so you are looking at a thermostat, a damper and your done.

At the risk of insulting mini-split lovers, I'm not going that way. I know they are efficient, etc., but my whole point for geo was no outdoor unit and relative stability of earth temps. I didn't install a 24k state of the art system (when it works) just to have to add an outdoor blower and 2ndary system. Ok...I'm done ranting. :-)

My location is just north of Philadelphia, PA.

I'll look into external sunscreens, maybe something with 50% reflectivity or thereabouts. I'm pretty sure the insulation is decent throughout. Impossible to remedy without major reconstruction, foam-fill, etc.

Adding a 3rd zone would be pretty easy. I have the thermostat already (a spare 3H/2C), the zoning panel accepts up to 4 zones (and I'm using only 2), and a single main trunk supplies that section of the house, although there two 8" feeds to the kitchen. I may be able to move the feeds somehow.

Hmmmm, balance dampers, or add a zone. I guess damper balancing would be a cheap quick fix, but wouldn't solve the problem of the room getting hot while the room with the thermostat is already satisfied. It would just provide more air when the system was on. I even keep the circ. fan on all the time, but the solar gain is incredible (great in the fall/winter/spring!).

I've been in buildings that are sometimes incapable of maintaining acceptable temperatures on both the north and south sides without active AC - ie, heat on one side and cooling on the other, both at the same time.

Yes, use a mini-split - but put the outside unit inside, in the cold area :-).

Posted By decafdrinker on 31 May 2012 06:50 AM
Not sure all the specs of the room, basically it's about 22x22 with a vaulted ceiling about 15 feet at the peak with a ceiling fan. One wall is part of the house, so just a doorway (double-width). The remaining 3 walls have between 4 or 6 Caradco Casement windows on each wall ( from 1991 (not sure the rating)) Windows are maybe 16x48 each. Only one wall of 6 windows faces south, and then one of the faces of the slanted roof (2 skylights) directly faces the sun. I know window film was installed, I'm just not sure where (I have a receipt from the previous owners, but it doesn't say which exact windows, and I can't tell from looking at them). Walls appear to be standard 2x4 with 1/2 drywall inside and plywood/wrap/vinyl siding outside. Roof is 2x8s.

I hate to cover them because the view is spectacular! Could I get/build some sort of EXTERNAL skylight shade? Maybe like a mini-exterior rack of angled slats that in winter would allow light but in summer with the sun higher would cast shadow?

I understand blocking the sun BEFORE it gets to the house would be ideal. Trees will take far too long, though. Decades!

Maybe trellises with vines in front of the south side of the house, and something fancy on the skylights to cast shade?

If the Caradco replacement windows are clear-glass double pane, assume they're between U0.5-0.6 with an SHGC north of 0.65. If they have a hint of a low-E tint you're probably in the U0.34-U0.42 range and an SHGC in the 0.5s.  I doubt Caradco made anything as low as 0.30 for a U-factor 20+ years ago.

The east and west facing windows usually have more summertime solar gain than the south facing windows due to the lower angle of the sun in the morning/evening and those are the sides where exterior shades would provide the biggest benefit.  They come in a variety of transparencies etc, but even some fairly bright versions cut the heat without totally killing the view:

http://interiordesigningblog.com/wp...shades.jpg

Cooleroo has a big chunk of the US market, but there are others (IsolRoll, Draper, etc.)  You can get motorized versions if you'd like to be able to roll them up to get a better look at the view without having to step out in the heat.

Low-E storm windows can be retrofitted on the east & west window, bringing the performance of a U0.50 clear-glass double-pane down to about U0.28-0.30.  Hard-coat low-E coatings used in storms have a faint brown or silvery tint that's pretty tame to look through compared to the blue stuff used on many high performance double-panes.

Window films are usually pretty obvious both visually and by feel, since they cut glare noticeably compared to clear glass or open windows, (some even darken the place considerably, and appear reflective on the exterior) and feel like the plastic they're made of.  Window films on the interior can sometimes damage the seal of double-panes by causing them to overheat, but that would not be an issue if installed on the exterior, but they're more subject to UV degradation and weather damage on the exterior.  Most get installed on the interior per manufacturers instructions.

On the south side overhangs & awnings work due to the higher angle of the sun, and the wintertime solar gain of the south facing windows might be worth leaving them as clear glass (depends- I'd have to model it in DOE2 or something for your specific location and shading factors to make that call, but it's generally true.)  Trellises or exterior shades can work there too, but at high noon most of the light & radiated heat  hitting the front surface of the window is reflected, unlike what happens on east west windows in direct sun.

Skylights are a mixed-bag, but on the south pitch the solar gains can be pretty intense in summer. Even interior shades and operable mini-blinds help, since it keeps the bulk of the heat gain at the ceiling level rather than letting it heat up the floor/furniture/people directly.  I haven't found a really good cheap exterior shading system that doesn't require going up on the roof, but there are snap-on versions out there if you want to google it.

Insulation ain't the issue. Window solar gain IS the issue.

What about stopping the ceiling fan?

If the volume in the high part of the room does not communicate with other rooms consider letting it stratify. The hot air will stay high and act as an insulator and heat storage medium. Think of it as a virtual attic - hot up there but you don't care since you don't occupy that volume.

Where north of Philly? I lived near Lansdale for 8 years and attended college in Easton.

The real problem again is design.
Load is never a problem for properly designed system.

One option is a geo console if you don't want the outdoor unit of the mini-split.

One option is balance (restricting air to the room with the Tstat keeps unit from cycling off early).

Best option as load will vary with clouds and from summer to winter is seperate zone if properly designed (is trunk adequate) with existing system or additional equipment. Do you even have capacity to cool all that air with existing system if you don't mitigate load? What is the potential peak load for this room?

I believe you can have your cake and eat it too, but you'll have to decide what the "cake" is. Solutions often require compromise.

Curt offers a valid point about stratification.

I'm leaning towards making it a separate zone. Some days, the entire rest of the house stays cool, but the sun room heats up. It would probably be better to have it's own zone, even if the t-stat is set up to only activate stage 1 to prevent excessive ramp-up of the blower. Might be a good first step.

A power damper would set me back $100 or so, and then just some wiring. I'll look up the duct sizes to be sure. It isn't a huge trunk but at least the same size as the upstairs Zone 2 trunk, which sometimes operates at stage 2 full-speed blower.

Out of curiosity, are the supplies in the floor or ceiling? Returns?

In the whole of downstairs, including the sunroom, everything is floor. There are 4 12x3 supplies in the sunroom in the four corners, and two returns approx 12x8 each at the end closest to the house. I know upper level returns and supplies would be great, but I don't think we can add that easily.

This is my plan...assuming ductwork sizing can handle air handler output at various stages/cfm. I think the minimum is 800 and the max is set to 1300 cfm.

Looks like a reasonable plan. Is it 3 zones or 4?

A way to handle a single small zone call whose ductwork can't quietly absorb all the low stage CFM output is to "crack" (elevate the zero stop) on one or two larger zones. I like the Belimo zone motors for this - it is easy to precisely set an elevated zero, the zone motors use just a coupl VA of power and they know enough to shut off at the end of travel.

The sunroom might be a good candidate to be cracked 10-20% open all the time...let it take 200 CFM or so to keep things quiet in other small zones.

I do not install bypass dampers.

I would put some care into balancing the supplies and returns such that you aren't pressurizing or depressurizing rooms. That causes infiltration and exfiltration which leads to heat loss and possibly wall moisture issues. Anything short of an open door will not self balance.

That applies to ANY duct system and has little to do with zoned supply system.