Covering Vents on Hoffman Enclosure

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fifty60

Senior Member
Location
USA
I have a Hoffman Enclosure that has forced ventilation vents. The vent for the intake is located on the side (width) bottom of the box. The exhaust vent is located at the top (width) side of the box. The vent openings are 5" by 5" square.

The enclosure itself is protected by rain/snow, but it is not protected from the outside temperature. I would like to block off the vents in the winter time. Does anyone know of a good way to do this? It does not need to be automated. Just a manual material to use to block the vents in the winter that will be easy to install and will not fall off.

The vents are not subject to any wind...
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
What about some magnetic rubber sheeting, assuming that the enclosure is made of ferrous material?
 

Smart $

Esteemed Member
Location
Ohio
Are these the punch-pressed type of slotted vents with outward protrusions?

Magnetic sheeting is not very malleable.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Are these the punch-pressed type of slotted vents with outward protrusions?

Magnetic sheeting is not very malleable.
If that is the case, you could put it on the inside where the metal is flat.

If you let it overlap enough on the outside you may be able to make it work, but you may not have enough width on the enclosure to get it it fit tight enough.
 

Smart $

Esteemed Member
Location
Ohio
If that is the case, you could put it on the inside where the metal is flat.

If you let it overlap enough on the outside you may be able to make it work, but you may not have enough width on the enclosure to get it it fit tight enough.
That's what I was thinking... but he mentioned forced ventilation vents. I'm thinking fan on the inside of at least one vent; filter holder on the other. If filtered, just wrap the filter with plastic wrap, or replace it with a piece of cut foamcore or such.
Something like a thermostat protector would work where fans are... if it didn't have the vents. :slaphead:
 
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fifty60

Senior Member
Location
USA
Thanks for the suggestions.

It has the vents for ventilation in the summer time, but it also has a heater to keep the inside of the enclosure above freezing in the winter time.

The entire enclosure is housed within another much larger enclosure. There is no worry of wind or water getting inside the enclosure, only hot or cold.

The hoffman enclosure is 36 X 30 X 8, and it has around 100W of live load inside of it, plus a 400W heater. My concern is how hard will the heater have to work in the winter time to keep the inside of the enclosure above 55 F. As mentioned earlier, the 36"X30"X8" is located inside of another much larger enclosure (like 5ft X 5ft X 5ft). There will be no wind hitting the vents.

I am worried about heat escaping through the vents by convection, making the heater work almost constantly to keep the enclosure above 55 F. The forced ventilation fans only come on at above 90 F. I was thinking of recommending that during the winter months, the intake and exhaust vents get covered, so then heat would only escape at a different rate through the covered vents through conduction.

My worry then is that for some reason the ventilation fan come on with the vents covered. That wouldn't be good either. Would probably have to disable the fan when the vents are covered.

I'm trying to make it as low maintanence as possible. The intake (fan) vent is located on the bottom of the enclosure, and the exhaust vent is located at the top of the enclosure. Maybe the only vent i would need to cover would be the exhaust vent located at the top of the enclosure, and the bottom intake vent could remain open. Does that seem reasonable?

Maybe with the enclosure being doghoused as it is inside of another enclsoure, where no direct wind is hitting the vents, the heater will not have too much trouble keeping the enclosure above 55 F even with the vents.
 

drcampbell

Senior Member
Location
The Motor City, Michigan USA
Occupation
Registered Professional Engineer
Put both the fans and exhaust vents at the bottom and add a baffle between the two, so that the air must be forced up & over the baffle before being exhausted. Now you don't have any free-convection heat loss, it doesn't require spring & fall maintenance, and it isn't vulnerable to someone neglecting to remove the covers for the summer.
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Unless your enclosure is insulated, it's not likely to make much of a difference in how much the heater runs. The steel will conduct the heat by radiation anyway. There are hinged louver vents you can get for the exhaust, so when the fan is running, the air pressure pushes them open to vent, but when the fan is off, they fall closed again. Generally we leave the intake vents open all the time even with those. If you seal it up too tight, moisture from condensation can't get out.
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
Thanks for the suggestions.

It has the vents for ventilation in the summer time, but it also has a heater to keep the inside of the enclosure above freezing in the winter time.

The entire enclosure is housed within another much larger enclosure. There is no worry of wind or water getting inside the enclosure, only hot or cold.

The hoffman enclosure is 36 X 30 X 8, and it has around 100W of live load inside of it, plus a 400W heater. My concern is how hard will the heater have to work in the winter time to keep the inside of the enclosure above 55 F. As mentioned earlier, the 36"X30"X8" is located inside of another much larger enclosure (like 5ft X 5ft X 5ft). There will be no wind hitting the vents.

I am worried about heat escaping through the vents by convection, making the heater work almost constantly to keep the enclosure above 55 F. The forced ventilation fans only come on at above 90 F. I was thinking of recommending that during the winter months, the intake and exhaust vents get covered, so then heat would only escape at a different rate through the covered vents through conduction.

My worry then is that for some reason the ventilation fan come on with the vents covered. That wouldn't be good either. Would probably have to disable the fan when the vents are covered.

I'm trying to make it as low maintanence as possible. The intake (fan) vent is located on the bottom of the enclosure, and the exhaust vent is located at the top of the enclosure. Maybe the only vent i would need to cover would be the exhaust vent located at the top of the enclosure, and the bottom intake vent could remain open. Does that seem reasonable?

Maybe with the enclosure being doghoused as it is inside of another enclsoure, where no direct wind is hitting the vents, the heater will not have too much trouble keeping the enclosure above 55 F even with the vents.

I had to design something of this sort to house fire alarm control panels in a non-conditioned space. Check the Hoffmann website, they have an on-line calculator that let's you design for various conditions so you can calculate what this is good for.

At first look, since this enclosure is inside another enclosure I'd SWAG that you don't need to worry about sealing the vents.
 

kwired

Electron manager
Location
NE Nebraska
Maybe with the enclosure being doghoused as it is inside of another enclsoure, where no direct wind is hitting the vents, the heater will not have too much trouble keeping the enclosure above 55 F even with the vents.
I think you are on the right track with that thought. 400 watt heater is more then enough to use as a space heater in a room much larger then 5x5x5.
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
I think you are on the right track with that thought. 400 watt heater is more then enough to use as a space heater in a room much larger then 5x5x5.

I found a graph here for heaters in Hoffman enclosures. Eyeballing it says that you need about 300 watts to keep the enclosure at 55 with the outside at 0, no wind. They say de-rate by 50% for windy conditions, and with an internal load of 100 plus the heater at 400 for a total of 500 watts, that puts you at 35 or so. Since this is inside another enclosure and wind conditions don't apply, the OP should be good to go.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I have on occasion used motorized louvers but really as another poster mentioned if the enclosure is uninsulated, insulation will do a lot more for you than closing off the vents, especially since there is no wind on it.
 

fifty60

Senior Member
Location
USA
Thanks. This was all very helpful. If I run into any problems this winter, I will look more at insulating the outside of the enclosure and less at covering the vents. Thanks!
 
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