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  1. Replies
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    very common in a lot of schools around here. ...

    very common in a lot of schools around here. thats the problem when you have a controls guy that doesnt know crap about what he's controlling. although its not always his fault...sometimes the...
  2. Thread: Exhaust

    by du mech eng
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    1
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    680

    consult your local mechanical code for minimum...

    consult your local mechanical code for minimum values. IMC says 75 cfm per fixture (urinal or toilet). i use that as my minimum. if its a very large bathroom with minimal fixtures in it i may bump...
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    sounds like you need a power exhauster. is there...

    sounds like you need a power exhauster. is there a lot of return ductwork in the system? barometric relief is best suited for systems with minimal return duct. your supply fan is pressurizing the...
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    this is a common misconception. in fact it is...

    this is a common misconception. in fact it is what i was taught entering the industry as well. take a look at the graph and the example in the link that jay guy provided. your system curve would...
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    most juristictions require a trap and a safewaste...

    most juristictions require a trap and a safewaste connection to a sewer pipe. check you're local plumbing code. what exactly is wrong with spilling the condensate to the roof and letting roof...
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    check out these two documents... ...

    check out these two documents...


    http://i100.photobucket.com/albums/m20/otsoccer15/TransformerLosses.jpg
    http://i100.photobucket.com/albums/m20/otsoccer15/PowerEquipLosses.jpg
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    505

    if you use a reverse return piping layout you can...

    if you use a reverse return piping layout you can manifold all of the wells together with one supply and one return from the house to the well field and the system will pretty much be self balancing....
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    probably a zoning issue. these diffusers are vav...

    probably a zoning issue. these diffusers are vav diffusers that use wax based thermal sensing element to that adjust a neck damper based on room temperature. i've heard of them being used to fix...
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    beauty shops have specific exhaust and makeup air...

    beauty shops have specific exhaust and makeup air requirements. dont want to be breathing in those fumes all day. do yourself and more importantly your wife a favor and sit down with a pro to go...
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    international mechanical code says 75 cfm per...

    international mechanical code says 75 cfm per fixture (whether it be toilet or urinal).
  11. Replies
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    1,497

    annexair, des champs, semco

    annexair, des champs, semco
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    there rate structure is tiered so you pay one...

    there rate structure is tiered so you pay one rate for the first 600kWH you use and another rate for additional power used. here's the PECO Tariff effective Jan 1st:
    ...
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    i think you've got it right. it can happen in...

    i think you've got it right. it can happen in winter if conditions are right but not gonna happen in the summer. i know i've read AIA & ASHRAE articles pertaining to this topic. might wanna try...
  14. Thread: VAV vs VVT

    by du mech eng
    Replies
    23
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    36,341

    gotta subscribe to hear this response

    gotta subscribe to hear this response
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    1,076

    Re: Yo, Doc...

    i get $1.31 to $1.35 depending on what value of btu i use for NG. either way balance point isnt 50deg.
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    thats one hell of a bottleneck. not ideal but...

    thats one hell of a bottleneck. not ideal but i'm guessing that unit could handle the static as long as the layout inside isnt as creative. is there some structural issue preventing them from...
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    by the way, you could also derive the following...

    by the way, you could also derive the following air side equations in the same manner as i did the water side above. just different units.

    Qtotal = 4.5 x CFM x Enthalpy Change
    Qsensible = 1.08 x...
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    the 500 is a conversion factor, not btu/hr. ...

    the 500 is a conversion factor, not btu/hr.

    the units are: (Btu x min)/(gal x hr x degF)

    here's a quick derivation:

    the basic equation for heat transfer is:

    q = mass flow x specific heat...
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    those numbers sound like nominal numbers for the...

    those numbers sound like nominal numbers for the tower. 95/85/78 is exactly what CTI uses for nominal rating of towers. it is possible however that those are the numbers that the system was...
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    its hard to tell because you are talking nominal...

    its hard to tell because you are talking nominal numbers here. depends on your local design conditions and the water temperatures you are looking for. dont forget the cooling tower has to reject...
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    wow, thanks for all of the responses. your...

    wow, thanks for all of the responses. your comments are exactly what i was thinking but it's reassuring hearing it from the guys doing the installations and servicing.
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    quick question for the residential pros. my...

    quick question for the residential pros. my girlfriend's mother is getting her furnace replaced and is looking to go with a 90% furnace. so far she's got one quote from the local utility and the...
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    yes, thats the industry standard assuming 0.075...

    yes, thats the industry standard assuming 0.075 lb/cu ft density for air and 0.24 specific heat. it comes from your original equation which was close, here's the derivation:

    q=m*cp*dt

    where:...
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    assuming: 25 students 1 teacher ...

    assuming:

    25 students
    1 teacher
    200 btu/hr/person sensible
    150 btu/hr/person latent
    lighting load = 1500 btu/hr
    no envelope heat transfer at 71/61 outdoor air
    ...
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    To elaborate on guru's comment; much like heat...

    To elaborate on guru's comment; much like heat moving from high temperature to low temperature, water vapor, like any other gas, will move from high pressure to low pressure.

    Summer Example:...
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