New UV air purifier installation question


  #1  
Old 01-17-12, 02:47 PM
S
Member
Thread Starter
Join Date: Jan 2012
Location: USA
Posts: 39
Upvotes: 0
Received 1 Upvote on 1 Post
New UV air purifier installation question

Howdy folks, my first time posting here, hopefully someone who is mechanically inclined with a bit of electrical knowledge can help me out with my quest for perfection

I bought this UV fixture to help keep my house free of mold:

AIR PURIFIER FOR AC DUCT UV Light TiO2 UVC AIR CLEANER | eBay

and installed it over the weekend. Great price, $600 less than the folks who installed my new gas furnace last Sept wanted to charge me for a nearly identical unit, one that also just plugs into a wall outlet - meaning it's on 24/7/365 whether it needs to be or not.

Ok, the cost of electricity isn't the big deal here, it's needing to replace the bulbs well before they would need to be replaced if the unit only came on when the furnace blower was running with no air passing over it, there's no need for it to be on. My A/C heat exchanger is tied into the furnace stack and uses the furnace blower for air distribution, all controlled with a programmable Honeywell thermostat.

Here's my brilliant idea: I want to tap into either the thermostat blower wires or the ones off the furnace (which might void my warrantee), put in a relay, and have the UV light come on automatically whenever the thermostat sends a command to the blower to turn on, or when the blower itself is receiving power.

How exactly would I go about doing this? Which wires from the thermostat would I need to tap into? Do I need a 5 volt or 12 volt relay? Is what I want to do even possible (dunno why it wouldn't be)? This is my thermostat model, a Honeywell UtilityPro model provided by BGE:

http://************/83mtcrf

The furnace is a Trane Two-Stage XV95 Gas Furnace w/variable speed blower.

Thanks folks, hoping to hear some bright ideas soon!
 
  #2  
Old 01-17-12, 02:52 PM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 4,469
Upvotes: 0
Received 1 Upvote on 1 Post
You can probably pigtail onto the blower motor connections one place or another. Any time the fan is operating the purifier would be energized as well.
 
  #3  
Old 01-17-12, 02:56 PM
S
Member
Thread Starter
Join Date: Jan 2012
Location: USA
Posts: 39
Upvotes: 0
Received 1 Upvote on 1 Post
I'm sure I *can* do it that way, power the lamp off the blower motor, but I'm worried about voiding the warrantee if I tinker with the brand new furnace.....prefer to switch off the t-stat command wires if at all possible, as in before they reach the furnace controller.
 
  #4  
Old 01-17-12, 05:29 PM
hvactechfw's Avatar
Member
Join Date: Jan 2011
Posts: 5,491
Upvotes: 0
Received 4 Upvotes on 4 Posts
does your new furnace control board have EAC terminals?
 
  #5  
Old 01-18-12, 07:12 AM
S
Member
Thread Starter
Join Date: Jan 2012
Location: USA
Posts: 39
Upvotes: 0
Received 1 Upvote on 1 Post
Erm.....what are EAC terminals? I haven't opened up the new furnace yet, but looking at the installation manual it appears that the controller is very similar to my old furnace's, in that it has a terminal block at the bottom - a row of screws with wires attached coming from the thermostat and going out to various components.
 
  #6  
Old 01-18-12, 08:07 AM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 4,469
Upvotes: 0
Received 1 Upvote on 1 Post
What is the make and model of the ignition control?
 
  #7  
Old 01-18-12, 08:44 AM
hvactechfw's Avatar
Member
Join Date: Jan 2011
Posts: 5,491
Upvotes: 0
Received 4 Upvotes on 4 Posts
You must open up the furnace and look for the control board and on the board look for terminals labeled EAC
 

Last edited by hvactechfw; 01-18-12 at 06:54 PM.
  #8  
Old 01-18-12, 05:57 PM
airman.1994's Avatar
Member
Join Date: Dec 2005
Location: VA
Posts: 5,491
Upvotes: 0
Received 8 Upvotes on 8 Posts
Uv lights are not going to keep your house free of mold. One uv light can not kill mold in the duct work air stream because there is not enoght contact time. You will need 8 plus feet of lighted duct to do this. You can kill mold on the coil with uv but you will need lights on both sides to do the job. Is your AHU UV protected?
 
  #9  
Old 01-19-12, 09:43 AM
S
Member
Thread Starter
Join Date: Jan 2012
Location: USA
Posts: 39
Upvotes: 0
Received 1 Upvote on 1 Post
Say what? I did a ton of research on UV air purifying systems after the furnace installer recommended I get one - I'm very allergic, especially to black mold - a serious household infestation almost killed me last year, no joke - organs started failing, got severe pancreatitis, which can be fatal.

Found the two problem spots (luckily, but very costly to remedy) and slowly recovered over the next 2-3 months. The first location was my deck door - the constant rain last fall during the hurricane and following storms rotted out the wood trim around the window and the frame filled with black moldy water - when I discovered the problem I got splashed with the moldy water and inhaled a ton of spores, that's what pushed me into the severe crisis. Had to order a custom replacement door, which took 6 weeks to arrive.

In between the door rotting and the new one arriving I had my new furnace installed. After they removed the old one I put on rubber gloves and a respirator to inspect the concrete floor for mold (basement has flooded multiple times from sump pump failures), found a bit of green mold but nothing bad - but when the furnace techs came back downstairs and I explained what I was doing they pointed into my heat exchanger and said "there's your mold problem!" - every surface in there was covered with black mold, and the drain line was just as filthy. They spent 2 hrs cleaning/sterilizing everything and replaced the drain line - said they have to do that kind of work in about 1 out of every 5 installs, it's a very common problem around here. But they wanted over $500 to install a dual lamp UV light system in the air return, and between the door/furnace double whammy I was totally tapped out, couldn't afford it then.

So I found and installed a dual lamp TiO2 system last weekend after doing plenty of research on that model (and others), primarily to kill any spores that leak into the house. I found tons of rave reviews from fellow mold allergy sufferers about how well that unit worked - are you telling me they're all victims of some massive placebo effect? I, for one, seriously doubt it.....I get sick within seconds of being exposed to black mold, if it's around I know! And what is an "AHU"?
 
  #10  
Old 01-19-12, 10:03 AM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 4,469
Upvotes: 0
Received 1 Upvote on 1 Post
>


Wow--- Sounds awful! Was this a condensing furnace (90% efficient using PVC pipe to vent?) Is your new furnace a condensing furnace?

Significant parts of condensing furnaces stay moist or wet by design, and parts of them are prone to getting plugged up with black mold.

Since you have a severe reaction to this issue, I think I might have suggested an 80% efficient furnace which avoids the moisture and condensing issues when it's properly installed.

How are you using the UV lights to control the issue? I presume your aim is to discourage mold growth on the surfaces of the heat exchanger rather than trying to kill mold spores that are entrained in the air.

Also, do you have central with a coil in the furnace? That is a place where moisture and condensation might tend to promote mold growth as well.


Frankly, I am not an Xpert on this kind of problem. I'm just raising a few issues you might want to consider.
 
  #11  
Old 01-19-12, 12:22 PM
S
Member
Thread Starter
Join Date: Jan 2012
Location: USA
Posts: 39
Upvotes: 0
Received 1 Upvote on 1 Post
Yes, central air, and both furnaces were/are high efficiency condensing models - one thing the installers pointed out was that the original 2 1/2" PVC vent line had been installed improperly, it was kinda level, drooped in one spot, not sloped towards the furnace like it's supposed to be (they fixed it) - I expect condensation built up in there perhaps? Don't know enough about that part of the system to know if it contributed to the mold problems or not.

As far as getting a non-condensing low efficiency furnace, not even on the table - live on a fixed income and utility bills seem to always keep going up, plus I got a $400 rebate for buying an Energy-Star furnace - a 10% discount on overall costs, was a great deal for me.

The A/C heat exchanger box sheet metal and the plastic drip pan located above the furnace were the most contaminated - the coils themselves were relatively clean - I used to brush them and blow compressed air over them periodically to keep the system efficient (thermal engineer by trade), but as I got sicker after a terrible basement flood on Xmas 2008 - that's when the mold problem got severe, wasn't aware of it at that time, of course - my maintenance activities dropped to nil, house started falling to pieces but I wasn't able to keep on top of things. If the furnace hadn't broke in March 2011 (17 yrs old) and the deck door hadn't rotted we'd have never figured out why my health was getting worse, not better - expensive way to find out, but it saved my life!

I put the UV light in the air return line, exactly at the point where the furnace guys said they'd install a system if I bought one from them - about halfway in between the vertical return line and the furnace, ~ 4-5 ft of ducting on either side of the horizontal run. Been doing some more digging online since I read airman's statement that UV lights don't do anything in the air return, and he's partially right, but it appears that even the experts don't agree on the matter!

I found another forum populated by furnace installers and everyone had a different opinion about various types of UV installations and their effectiveness, but one thing was plainly apparent from other website's data - the energy need to destroy mold spores is an order of magnitude higher than the output of any available residential UV system, although they *can* damage the DNA, which might prevent reproduction. The UV can definitely kill bacteria, although it may take multiple passes through the system to get everything - my house is relatively airtight for the most part (good and bad), so the lights will definitely help somewhat....

.....but, the biggest source of the problem lies in the constantly damp heat-x box during A/C season, as you mention. After more digging, it would appear that I need two more separate lamp systems in there to prevent a re-occurrence of mold growth, one on each side of the coil V, lights mounted above the fins. But there's a potential problem with that - constant UV exposure on the plastic drip pan can destroy it over time, a disaster.....so if I do decide to install them in the spring, I'll also need to put in some aluminum reflectors to block the light from reaching the pan....might be more work than it's worth.....spraying a bleach-based mold killer inside the box periodically might be a heckuva lot easier and less expensive in the long run, and that would also clean out anything in the drip pan/drip line too.

BTW, I found a solution to my original question (too late?) - Honeywell makes "Smartlamp" UV systems with airflow sensors, so the bulbs light up when the blower is running, then turn off 30-40 minutes later, greatly prolongs bulb life - for another $100 I could have bought one of those instead of the "dumb" one I got. That model also can run off the thermostat commands, your choice, very nice units. Might just buy one of those, swap it out with the existing one, then put the current one in the heat-x box and only run it over the summer.....I can live with that....we'll see....
 
  #12  
Old 01-19-12, 01:00 PM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 4,469
Upvotes: 0
Received 1 Upvote on 1 Post
You obviously now have an excellent grasp of the problem and have a variety of means to deal with the problem.

I would say that inspection and maintenance would be your other main defense. Checking the condition of your system in the spring and fall would be a good idea, looking for any evidence of contamination. Spraying with a bleach solution would help supplement other means of avoiding problems.

To aid in such maintenance. you might want to cut holes in the sheet metal to allow the AC coil to be inspected and treated easily. I might experiment with a 1 gallon sprayer with a wand to spray your bleach solution and incidentally help clean the coils and duct work.

In addition, I'd take the inducer motor assembly out of the furnace, which gives access to the bottom of the heat exchanger, and use that point of access to pour some bleach solution into the condensing part of the furnace.

Often there is a plastic trap which prevents air from getting into the condensing portion of the furnace --- that tends to get plugged with black mold. Rinsing that out and hitting it with some bleach solution might be worth trying.

When you get some experience with inspection and maintenance you will have a better idea of how much is worth doing and how often. I'd start out by doing a lot and then you can cut back if that seems reasonable.
 
  #13  
Old 01-19-12, 03:31 PM
S
Member
Thread Starter
Join Date: Jan 2012
Location: USA
Posts: 39
Upvotes: 0
Received 1 Upvote on 1 Post
Wow, excellent idea, that never occurred to me! Only issue I can think of off the top of my head is I'll need to be extremely careful with the saw depth (will probably use a jig saw, easier to control than a Sawzall) so I avoid damaging the fins, or even worse, puncturing a coolant line....going thru the back panel would give me the best access, but that gives me very little leeway for depth of cut since the V is the same distance from the panel vertically, as opposed to going in from one side, where I'd only get close near the bottom (mucho clearance at the top as the coils are tilted away from the sides).

Any tips on controlling the blade depth besides building a jig from 2 x 4's or something similar and mounting that to the panel for the saw to track? I can tilt the blade somewhat to make it shorter, but nowhere near far enough so that there's no risk of the blade hitting something while at the long stroke of the cycle. Also could use a power grinder metal cutting head, but that would make a helluva mess and shoot sparks of hot metal all over my woodpile/storage rack.....not too bright of an idea, to say the least!

I have almost every kind of hand power tool known to man (almost :-), so I have lots of tools to pick from if you can think of which one would be best (I'm running out of steam here, been a long day) - I used a Dremel tool to cut the hole in the ductwork to install the UV light, but would burn through an entire jar of cutting wheels using that thing, and it would take forever too. I'm assuming the sheet metal would be too thick for tin snips to cut through?
 
  #14  
Old 01-19-12, 04:18 PM
Grady's Avatar
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 12,682
Received 41 Upvotes on 39 Posts
You may be able to rent a pair of power snips at your local tool rental store. That's what I use to cut out the side of a furnace for the return duct connection. The ones I use are similar to the ones pictured here: DEWALT DW891 Heavy-Duty 14 Gauge Swivel Head Shear | ToolBarn.com

On the subject of damage to the plastic drain pan, I'd suggest replacing the plastic with a stainless pan which can be made by nearly any good sheet metal shop. The last one I had made cost less than $100.
 
  #15  
Old 01-19-12, 04:32 PM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 4,469
Upvotes: 0
Received 1 Upvote on 1 Post
Aviation hand snips would be what I'd try. They should do fine on duct work.
 
  #16  
Old 01-19-12, 04:54 PM
Grady's Avatar
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 12,682
Received 41 Upvotes on 39 Posts
If it's an ordinary sheet metal plenum the hand shears are fine. I was thinking about a cased coil. I guess if it were a cased coil, it would have an access panel. duh...
 
  #17  
Old 01-19-12, 06:32 PM
airman.1994's Avatar
Member
Join Date: Dec 2005
Location: VA
Posts: 5,491
Upvotes: 0
Received 8 Upvotes on 8 Posts
Let me add another rock in the pile! Imo installing a dehumidifer to the system will be better money spent than the IV light. If you can set it up so in AC mode you have a down period with the fan blowing so the AHU (airhandler) can dry out. And in heating keep the fan on 24/7. The deu will be for no load times spring and fall to keep the RH below 55% this should keep it dry so u don't have a mold issue. IMO this is preactive rather than having a mold issue then trying to take care of it I have been doing IAQ work for 17 plus years I have tons of pictures of mold in AHU's in hospitals that have UV lights
 
  #18  
Old 01-19-12, 06:36 PM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 4,469
Upvotes: 0
Received 1 Upvote on 1 Post
Interesting idea airman. I presume that the A/C coil is the biggest problem for mold growth in a typical home system.

Where would you put a dehumidifier in the system to avoid a mold problem?
 
  #19  
Old 01-19-12, 07:36 PM
airman.1994's Avatar
Member
Join Date: Dec 2005
Location: VA
Posts: 5,491
Upvotes: 0
Received 8 Upvotes on 8 Posts
You can take supply air or air from the space for the air entering the dehu. Exhaust air can be ducted to the retun of the HVAC system. Would be best to instal this into the return box. I'd add that you will need a good dehu to handle the low temps of the supply air. Like a therma stor.
 
  #20  
Old 01-20-12, 01:33 PM
S
Member
Thread Starter
Join Date: Jan 2012
Location: USA
Posts: 39
Upvotes: 0
Received 1 Upvote on 1 Post
I do have a dehumidifier in the basement, sits right next to the sump - unfortunately my ancient heavy-duty Sears model broke (thing must have weighed 70-80 lbs!), the auto-defrost mode quit working so it kept freezing up, gave it away to a fixer-upper guy and bought a new one. Which unfortunately, while being a comparable lightweight with wheels and a carry handle, is a power hog.

When I got it my electricity bill jumped $20-$30/month, was stumped at first why until I bought a Watt-a-meter and hooked it up to the unit, basterd was sucking up juice at a ridiculous rate! Dialed it back to 45%/low blower mode to tame it's consumption, much better now.

So knowing that, buying a whole-house system for the A/C mode (the coils of the A/C unit are basically a dehumidifier anyway) would:

1) Probably cost a lot of money for a quality unit.
2) Be a difficult install for a single physically limited person.
3) Cost a ton of money to run during A/C season (MD is infamous for it's 90%+ humidity during the summer), especially if the hot exhaust is dumped into the return air flow.
4) Would add another place where mold would love to grow!

It's a good idea for commercial use, just don't think it scales well to a small residential home. Cutting out a panel in the air handler/coil box to allow for regular inspection and cleaning is by far the simplest/cheapest option IMO. In fact, after I discovered the disaster in there I was b*tching to a friend of mine (also an engineer) about why systems aren't designed for easier maintenance, both the heat-x box and the drain tube - as in the front panel should be two pieces so you can remove the drip pan for cleaning and get access to the coils - we had to saw the single panel in half to remove it without cutting the A/C freon lines. Stupid!
 
  #21  
Old 01-20-12, 04:33 PM
airman.1994's Avatar
Member
Join Date: Dec 2005
Location: VA
Posts: 5,491
Upvotes: 0
Received 8 Upvotes on 8 Posts
A good unit will have twice the humidity removal that one of your units has at half the electric used. Thes are residential units that's what they are designed for. They also have merv 11 filtration. Yes an AC will dehumidify but it does nothing for u in no load times are when your pump dies again.
 
  #22  
Old 01-20-12, 05:18 PM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 4,469
Upvotes: 0
Received 1 Upvote on 1 Post
Hello airman,


Suppose you put one of those heavy duty dehumidifiers ahead of the AC coil. What's the affect on how the AC coil operates and it's efficiency?
 
  #23  
Old 01-20-12, 08:22 PM
airman.1994's Avatar
Member
Join Date: Dec 2005
Location: VA
Posts: 5,491
Upvotes: 0
Received 8 Upvotes on 8 Posts
It can be done and it would be no different than placing it on the return side. But I have never liked the idea of using a small fan 200 cfmish to blow into duct that has a fan blowing 800 - 2000 cfm of air.

The biggest thing is to dry the coil after the AC has run to prevent mold. This can be done with the AHU but the coil and pan can hold up to 8 pounds of water. That's going back into the air that's when the dehu is needed
 
  #24  
Old 01-22-12, 07:43 AM
S
Member
Thread Starter
Join Date: Jan 2012
Location: USA
Posts: 39
Upvotes: 0
Received 1 Upvote on 1 Post
"the coil and pan can hold up to 8 pounds of water"

A gallon? How is that physically possible? My drip pan is ~ 17.5 x 21.5 x 1, lessee.....that's 376.25 cu inches, convert units.....oh my god, you're right.....if the drip pan is full (assume a clogged drain line), that's 1.6 gallons and 13.3 lbs of water! And that number doesn't include droplets of condensation on the fins and coils either......wow....

But being a strong believer of the KISS method of thinking when at all possible, I still think regular maintenance is the best solution by far - the furnace guys installed a T fitting in the drip line for me so I could pour bleach into the line to clean it, but I went a step further - I installed a ball valve near the bottom of the line right before it enters the floor drain so I can backfill the line *and* the drip pan with bleach and let it sit for a minute or two to ensure it covers all surfaces and kills any bacteria or mold. That job should be done at least once a year, preferably before and after the A/C season.

As far as my plan to cut an access hole in the coil box to make it easier to clean, I checked a few things yesterday to see what I can do and what I need:

1) The box is made of the same material as the original furnace, heavy gauge sheet metal with a baked enamel finish, sorta light green.

2) I saved both front access panels from the old furnace, I always save stuff like that for recycling the materials for other uses (sheet metal is pretty pricey). I tried cutting what's left of the smaller panel (already used part of it) with all 3 of my tin snips, but even the heavy duty one with perpendicular blades were useless, couldn't cut it, so I'll be needing the power snips you recommended or a power saw of some type.

3) I had a moment yesterday while getting PT - why not make the cover panel out of clear 1/4" acrylic so I can look inside to inspect the coils and drip pan without potentially exposing myself to mold? If I see crud, I can safely gear up before removing the panel. And it would also have sufficient structural strength, wouldn't need to put a doubler plate on it or any other type of reinforcing.

All I have to do is find a place to buy it, but have no clue where to even start - anyone have any ideas where to look? Doesn't necessarily have to be acrylic, any clear plastic will do.
 
  #25  
Old 01-22-12, 08:09 AM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 4,469
Upvotes: 0
Received 1 Upvote on 1 Post
Originally Posted by sts_66
[


3) I had a moment yesterday while getting PT - why not make the cover panel out of clear 1/4" acrylic so I can look inside to inspect the coils and drip pan without potentially exposing myself to mold? If I see crud, I can safely gear up before removing the panel. And it would also have sufficient structural strength, wouldn't need to put a doubler plate on it or any other type of reinforcing.

All I have to do is find a place to buy it, but have no clue where to even start - anyone have any ideas where to look? Doesn't necessarily have to be acrylic, any clear plastic will do.

Excellent idea! Around here a variety of specialized distributors or good hardware stores would probably have material that would be suitable, and some might be able to cut it to size for you. I'd look around for plastic distributors and shop around.

Some experience will tell you what kind of methods you need. If twice annual inspections and bleach treatments are an unreasonable nuisance or aren't doing the job adequately, then more elaborate methods such as those suggested by airman might be tried. If the bleach treatments do the job, then they do the job and are satisfactory by themselves.

In my experience as a repairman, there is a LOT to be said for adequate inspection and maintenance. Most homes don't get much of it, and you've experienced examples of the downside of that.
 
  #26  
Old 01-22-12, 09:56 AM
S
Member
Thread Starter
Join Date: Jan 2012
Location: USA
Posts: 39
Upvotes: 0
Received 1 Upvote on 1 Post
Did some googling, Grainger sells all sorts of plastic panels, and there's a store just 10 minutes from my house, it turns out - never knew it was there, it's hidden in an industrial park out of view, although I must have driven past it literally thousands of times since I've lived here! (it's off the main east-west highway in this area)

I've narrowed in on PETG plastic, can get a 24" x 24" panel for around $30 - after reading about various types (Lexan, acrylic, polycarbonate, etc) it would appear that a lot of them, while having good tensile strength, aren't exactly easy to cut and drill without cracking. Now that I think of it, I have a scrap of 1/16" clear plastic, material unknown but likely acrylic, and every time I've tried to cut off a piece I end up cracking it while cutting regardless of what type of tool I use, frustrating as hell and very wasteful, takes multiple efforts until I get lucky and get a clean cut. The PETB is clear, strong, UV resistant (in case I ultimately decide to install a UV light in there), and is easily cut/formed/machined without cracking.

Think I'm all set now as far as that goes, no rush on the job either, just need to get it done before April.
 
  #27  
Old 01-22-12, 10:03 AM
Houston204's Avatar
Forum Topic Moderator
Join Date: Oct 2009
Location: Texas
Posts: 6,530
Received 95 Upvotes on 88 Posts
If you will be installing this in the supply side of the evaporator coil, are you going to insulate over this plastic to prevent organic growth in the cooling mode?
 
  #28  
Old 01-22-12, 12:49 PM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 4,469
Upvotes: 0
Received 1 Upvote on 1 Post
Hello Houston,


Mold or organic growth on the plastic might be a useful tell tail indicator that it's time to get in a spray bleachy solution around. Or you could easaily add a flap of insulation on the outside to reduce heat flow that might encourage condensation.


I'm guessing plastic would be relatively resistant to heat flow and condensation compared with sheet metal. Plastic and some insulation would be worth a try would be my guess, and more elaborate methods used if they proved to be needed.

I might try putting some kind of self adhesive gasket like material around the edge of the plastic and then mounting it inside the sheet metal so that air pressure is pushing the plastic against the sheet metal to seal it, rather than pushing the plastic away from the sheet metal if it were mounted outside.
 
  #29  
Old 01-22-12, 01:43 PM
Houston204's Avatar
Forum Topic Moderator
Join Date: Oct 2009
Location: Texas
Posts: 6,530
Received 95 Upvotes on 88 Posts
I'm confident that uninsulated plastic would not stay transparant very long in the supply side.

I'd predrill holes in the plastic panel and secure from the outside with screws and foam tape. Some duct wrap (insualtion with a vapor barrier) would help prevent the formation of condensation.
 
  #30  
Old 01-23-12, 07:38 AM
S
Member
Thread Starter
Join Date: Jan 2012
Location: USA
Posts: 39
Upvotes: 0
Received 1 Upvote on 1 Post
Guys, it was probably lost in the shuffle, but as I mentioned previously I'm a thermal engineer.....used to work for NASA and then a contractor designing two-phase thermal control systems for Hubble, the ISS, and various observatories/satellites.....not really worried about potential condensation problems on a plastic access panel.

Of course I'd use a thin foam weatherstrip gasket to seal it and sheet metal screws to mount it, don't really think a rigid foam insulation cover is necessary but I have scraps of a 1" foam panel leftover from another project if it turns out I do need one.

As SP mentioned, the thermal conductivity of plastics are several orders of magnitude lower (as in a thousand times less) than the existing sheet metal box, so the cover plate would be the last place I'd expect condensation to form on - and although my memory of what the inside of the box looks like is a little fuzzy (was quite ill from mold when they installed the new furnace), I don't think there's insulation on the inside - in fact, from a design viewpoint, putting insulation inside would be downright dumb seeing as it would be waterlogged all the time, negating it's functionality.

But this does bring up an interesting thermal efficiency question: how much cooling capability is lost via ambient environment heat flow into the heat-x box while the A/C is running, which is increased by the air flow over the relatively hot metal sides? A fellow I went to grad school with ended up working for Trane, ironically......IMO if heat leaks into the box were significant enough to alter the efficiency by a measurable amount we'd all have water heater type blankets around the boxes, but we don't.....therefore the effects must be negligible....and thinking about it from another POV, the lack of condensation on the exterior walls of a typical installation proves this theory out.

Man, my brain is not operating well this morning....and it's not because I'm hungover from that terrible last second Raven's loss last night....damn, almost burst out in tears when Cundiff missed that FG....but I digress.....just realized that it's impossible for condensation to form on the walls......they're the hottest part of the heat-x box, therefore no water vapor would condense on the walls, inside or out.....all the water will condense on the coldest components, which are the coil tubes first, the fins second, but rarely, if ever, on the walls themselves.

Ok, just had a flashback - when I (very briefly) looked into the contaminated box I saw black mold on the top and bottom seams, but none on the walls - and that makes complete sense: when the A/C unit shuts off air in the hotter basement would be drawn to the much colder components in the box, through the seams, because of the partial pressure differentials, and water vapor would likely condense at the first colder surface it hits, which is right there on the inside walls at the seams, which is what I observed.

Hmmm....."partial pressure differential" may not be the correct term, now that I think about it......lessee if I can put this into words, then the appropriate terminology might come to me....to start off, all molecules "prefer" to be in their lowest energy state, one of the laws of thermodynamics IIRC. Water vapor is a higher energy state than liquid water because it took 1 calorie/gram to evaporate it...erm, no, that's not correct, that's the amount of energy it takes to heat a gram of water by one degree.....ok, the latent heat of vaporization/condensation is ~ 600 cals/g of water (yes, I had to google it, have forgotten so much stuff it's not funny)....oops, I'm going off course again, the numbers aren't relevant to the discussion. Let's just say heat flows downhill, ergo hot air will seek cold objects, just as high electrical potential energy objects want to seek ground, which is zero potential energy [Note: this is not the same as saying "heat rises" - that's a buoyancy effect, hot air is less dense (lighter) than cold air, but we're talking about water vapor content here, not densities.]

Also, nothing short of a solid hermetic seal can completely prevent this water vapor/energy transfer - nature (physics?) is relentless when it comes to things like this, and that's especially true for thermal expansion/contraction, as in nothing can stop it from occurring - it's also a tremendously powerful force - think of how what you'd think as relatively weak ice being able to crack much stronger granite and concrete with ease.

Does all that make sense now? Guess I'll have to post it and reread it once or twice to make edits, I'm sure the first draft won't be as good as it could have been......

P.S. In the end, I edited that post 5 frigging times, give up, it's good enough.....
 
  #31  
Old 01-23-12, 08:37 PM
Houston204's Avatar
Forum Topic Moderator
Join Date: Oct 2009
Location: Texas
Posts: 6,530
Received 95 Upvotes on 88 Posts
Rereading the original post I see that this is the return air side as apposed to the 55 degree air side.

Why is it going to be waterlogged all the time?
 
  #32  
Old 01-24-12, 10:19 AM
S
Member
Thread Starter
Join Date: Jan 2012
Location: USA
Posts: 39
Upvotes: 0
Received 1 Upvote on 1 Post
No, I think you got a little confused over how the thread started and where it evolved to - the UV air purifier was installed on the return side, then I started considering installing another light in the heat-x box, then had the idea to cut an access panel in the rear of the box to give me access for regular coil/fin cleaning, and to make the cover from clear plastic so I could easily inspect it without needing to open it up.

Putting insulation on the inside of any kind of heat transfer box is useless, it needs to go on the outside to prevent heat exchange with the ambient environment. In this case, when the A/C is running in a high humidity region, the air inside the heat-x box is so full of water vapor everything inside is constantly soaked when the A/C is running, although the walls of an uninsulated box would likely dry out after the A/C has been off for a while, heated up by the hot(ter) air wherever the unit is located. In fact, now that I think about it, that's a great reason NOT to insulate that box - it would rust out and/or be extremely moldy if the walls weren't allowed to heat up and dry off.

Also, almost all insulation is based on creating "dead air" pockets - the thermal conductivity of air, or any other gas for that matter, is thousands of times lower than solids - so to make a good insulator, you'd want to use the lowest thermal conductivity material you can find (fiberglass or foam, for instance), make it as thick as possible, and very "airy", i.e. a low density - the more air it can trap the better it will work. Closed cell insulators are the best types to use where condensation may be a problem because they won't fill up with water, which has a very good thermal conductivity compared to air - entrapped water would short circuit an open-cell type insulator.

Other terrestrial types of insulation include things like shiny mirror-like foils used in attics to reflect IR radiation from hot roofs back outside instead of heating up the air in an attic. In the vacuum of space, all insulation is made of reflective materials separated by tiny gaps, since you don't need to worry about the conductivity losses from air or water, of course - but creating those thermal blankets is literally an art - almost all of them a hand made and unique, unless they're going into a system like the GPS satellites - in that case every satellite is pretty much identical so you can make templates to mass produce the exact same blanket multiple times.

Which jogs my memory about another common item that also depends on the lack of air to create a great insulator - a thermos. The good ones are made from a metal shell with a very thin reflective glass inner shell, a vacuum in the gap between the two shells, and the only contact between the shells is the seal at the top where the glass and metal meet around the rim. Add it all up, and you have meet all the requirements for a great insulator: very low direct conductive losses, no conduction via air, and very low IR heat transfer - in or out.
 
  #33  
Old 01-24-12, 04:51 PM
Houston204's Avatar
Forum Topic Moderator
Join Date: Oct 2009
Location: Texas
Posts: 6,530
Received 95 Upvotes on 88 Posts
I have serviced thousands of systems and understand the function of fiberglass, but thank you for that interesting article. Ductwrap is fiberglass with a vapor barrier.

If the heat-x box you refer to is a supply air plenum I would be interested to hear if it does not condensate this summer without insulation over the outside of it.
 
  #34  
Old 01-24-12, 07:24 PM
Grady's Avatar
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 12,682
Received 41 Upvotes on 39 Posts
I'm with you Houston. Unless there's some kind of insulation, I'd bet dollars to donuts, it'll sweat. I've been wrong before & surely will be again but I don't think this will be the time.
 
  #35  
Old 01-25-12, 10:11 AM
S
Member
Thread Starter
Join Date: Jan 2012
Location: USA
Posts: 39
Upvotes: 0
Received 1 Upvote on 1 Post
Sorry if my previous post sounded a bit, what's the right word....condescending? It was more of a mental exercise to stimulate my brain, which doesn't get used a whole lot these days as far as thermal engineering and design goes....haven't worked for over 5 yrs because of various health problems.

The box *is* on the supply side, sits above the furnace, and as far as insulation on the box, there's definitely nothing on the outside, but to be honest I can't be 100% sure there's absolutely nothing on the inside - but I do know there's nothing on the front panel because like I mentioned before I sawed that in half myself so the furnace guys could pull the coils out to clean the mold.

I've never seen condensation on the walls either.....could be a double walled box I guess, but then you'd think the front panel would sweat, right? I've always had a dehumidifier running in the basement so the humidity never gets above 40%, maybe that's why? Hang on, let me go take a quick look at it.....

.....ok, I removed a couple screws from the front panel and bent back an edge, there's definitely scraps of what looks like some kind of very damaged yellowish fiberglass insulation, but it's almost totally destroyed - exactly why I said earlier it shouldn't be inside and constantly getting soaked with water - not only does that make it less efficient as an insulator, over time the water destroys it. Bits of insulation crumbling off the walls is probably what has clogged the drain tube/drip pan outlet several times, causing spillage down the sides of the old furnace - it was a mess, especially in the front where the drain line connects - there's a 12" wide shelf-like surface on the top of both furnaces, i.e. the heat-x box is square but the larger furnace is rectangular .
 
  #36  
Old 01-25-12, 12:36 PM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 4,469
Upvotes: 0
Received 1 Upvote on 1 Post
Insulation inside duct work is common, especially on better quality installations. The usual purpose is to reduce motor and air flow noise.
 
  #37  
Old 01-25-12, 04:14 PM
Grady's Avatar
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 12,682
Received 41 Upvotes on 39 Posts
Most of the factory evaporator coil cases are insulated on the inside with fiberglass. Some is foil covered as a vapor barrier, most is just coated fiberglass.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: