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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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    754

    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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    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...
  10. Replies
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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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    1,626

    annexair, des champs, semco

    annexair, des champs, semco
  12. Replies
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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
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    39,672

    gotta subscribe to hear this response

    gotta subscribe to hear this response
  15. Replies
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    1,224

    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.
  16. Replies
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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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    1,199

    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
    ...
  25. Replies
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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:...
  26. Thread: HRV

    by du mech eng
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    763

    robo, i think you are trying to say the same...

    robo,

    i think you are trying to say the same thing but since the wheel is not 100% efficient it can only precondition the fresh air so much. whatever type of heating and cooling you have must...
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    have to agree with gruvn here. although it does...

    have to agree with gruvn here. although it does not control as well or over as wide a range as a txv, a cap tube will compensate for variations in load.
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    is that a residential number?

    is that a residential number?
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    seems like overkill to use for only a few months...

    seems like overkill to use for only a few months of the year. what kind of heat is availible on site? how much ventilation are we talking about?
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    Re: To Du Mech

    i'm not quite sure i understand this. how is it more efficient to heat up ventilation air that is meant to dissipate heat? all you are doing is taking the heat from the motors, that you are trying...
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    why would you use an hrv to ventilate an...

    why would you use an hrv to ventilate an unconditioned space? there is no energy to recover if you are not putting any energy in. also what kind of space is this that doesnt require any heat?
    ...
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    methods outlined in ashrae fundamentals handbook....

    methods outlined in ashrae fundamentals handbook. actually trane trace 700 does it for me but it uses the methods outlined by ashrae.
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    we typically call out for pvc or copper and our...

    we typically call out for pvc or copper and our detail drawing shows a T with a cleanout. as far as pipe size, i use the following that was given to me by my boss when i first started working, i've...
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    i vote for geothermal heat pumps with hot gas...

    i vote for geothermal heat pumps with hot gas reheat to control humidity. as brent said, you could run your radiant off them as well as domestic hot water. but definitely get a reputable design...
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    oops [Edited by du mech eng on 07-14-2005 at...

    oops

    [Edited by du mech eng on 07-14-2005 at 12:41 PM]
  36. we used ductsox brand on a recent project because...

    we used ductsox brand on a recent project because a client requested it over spiral. this is the first cooling season and no complaints so far.
  37. Replies
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    2,072

    ferris state is supposed to be the best for the...

    ferris state is supposed to be the best for the hvacr field.

    http://www.ferris.edu/cot/hvacr/
  38. Replies
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    this is exactly right. the mca is typically 1.25...

    this is exactly right. the mca is typically 1.25 x the full load running amps of the unit. mocp is typically around twice the full load amps. both should be readily availible from the manufacturer...
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    i think he's saying assume the R value of the...

    i think he's saying assume the R value of the soil is zero. you still have the r value of the roof.
  40. Thread: Ductwork

    by du mech eng
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    1,254

    as long as the flex is accounted for in the...

    as long as the flex is accounted for in the design and installed properly its perfectly fine.
  41. Replies
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    yes, that was my point. guess i should have been...

    yes, that was my point. guess i should have been more clear
  42. Replies
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    2,312

    again not related to refrigeration but for some...

    again not related to refrigeration but for some reason it drives me insane when someone uses the term "for all intensive purposes"
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    i'd like to see some support of this statement. ...

    i'd like to see some support of this statement. we do these types of systems for schools all the time. i've done several life cycle cost analyses and usually see simple payback periods around the 6...
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    http://www.bigassfan.com/

    http://www.bigassfan.com/
  45. marauderx, where can i find a copy of your...

    marauderx,

    where can i find a copy of your paper? i am also a design engineer and i get into a decent amount of geothermal work. i'm always looking for technical papers on the subject and i'd...
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    i've read most of these posts and they all make...

    i've read most of these posts and they all make good points. it all depends on what you are looking for. one thing i would like to recommend is try posting this question in an engineering forum as...
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    excellent, thanks for the input

    excellent, thanks for the input
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    683

    From my internet research what I've gathered is...

    From my internet research what I've gathered is they are the same stuff except diesel fuel for road use has more stringent standards and is taxed higher. Any one have any experience here? Can #2...
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