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  1. #1
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    Question: How to Make Condo MAU More Energy Efficient?

    First time poster on this forum. Not sure if I should be posting in the residential or commercial section.

    My questions are about a make-up air unit (MAU) for a small condo building (12 apartments) where I live, in Canada (i.e. cold climate). The building is a four story wood framed structure built in 1979. The MAU is an Engineered Air model S225/O/R which feeds air to three hallways in the building, pressurizing them slightly.

    Myself and some of the other owners are interested in optimizing the energy efficiency of this MAU, and the building in general. So I want to educate myself on what the options are so that I can discuss the issue intelligently with a professional.

    My questions:

    1) What considerations should be made in determining the hallway temperature set-point for the building?

    2) What is the typical range of temperature set-points for hallway air supplied by an MAU.

    3) Are there any code requirements for the temperature of condo building hallways?

    4) Is it possible to change the air flow rate from an MAU? If so how is this typically done?

    5) Are there any code requirement for the air flow rate to hallways from a MAU?

    6) Are there any other common ways to make a standard MAU operate more energy efficiently?

    Any suggestions would be appreciated.

  2. #2
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    Thread Starter

    How to Make a MAU More Energy Efficient?

    I live in a small condo building. Myself and some of the other owners are interested in improving the energy efficiency of the building. One of the things we are considering is adjusting the temperature and/or air flow rate from a make-up air unit (MAU) that supplies air to the building hallways.

    With respect to this, the questions I have are:

    1) Other than the comfort level of the temperature in the hallways, are there any other factors that we should be considering?

    2) Is there a simple way to adjust the air flow rate from a MAU?

    3) Are there any other common ways to make a standard MAU operate more energy efficiently?

    Any suggestions would be appreciated.

  3. #3
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    The make up air unit's purpose is to replace the air that is being sucked out of the building by things like bathroom or kitchen exhaust fans, dryers, and gas burning appliances. I have also heard that maintaining a slightly positive building pressure can help keep out bugs. If a building is in a negative, things such as natural draft water heaters and boilers might not draft correctly and could cause a dangerous carbon monoxide situation.

    Ideally a building's pressure should be neutral to slightly positive. In my experience though, most buildings instead seem to be in a slight vacuum.

    How is your building? You probably don't want to hear this, but you likely should be thinking of increasing the blower speed, not slowing it down.

  4. #4
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    Thread Starter
    Quote Originally Posted by ammoniadog View Post
    The make up air unit's purpose is to replace the air that is being sucked out of the building by things like bathroom or kitchen exhaust fans, dryers, and gas burning appliances. I have also heard that maintaining a slightly positive building pressure can help keep out bugs. If a building is in a negative, things such as natural draft water heaters and boilers might not draft correctly and could cause a dangerous carbon monoxide situation.

    Ideally a building's pressure should be neutral to slightly positive. In my experience though, most buildings instead seem to be in a slight vacuum.

    How is your building? You probably don't want to hear this, but you likely should be thinking of increasing the blower speed, not slowing it down.
    I think we have pretty good positive pressure in our building. If I put my hand at the bottom of the entrance door to my apartment, I can feel air blowing lightly underneath the door from the hallway.

    In fact I am thinking there is too much positive pressure. The MAU was not working for a week or so in October this year. During this time I noticed that my apartment was about 2 degC (4 degF) cooler during the night. I figure this was because the MAU pushes warmed air continuously into my apartment from the hallway when it is working.

    I would like to set it at the minimum acceptable temperature and flow rate, to save some money on heating the air and to have better control of the temperature in my apartment. The temperature is easy to adjust, but the flow rate I don't know if there is a way to do this. And for both temperature and flow rate I'm not sure if there are code requirements as to what the settings must be.

  5. #5
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    It needs to be looked at by someone who can "see" the whole building picture. Mechanical as well.
    Small MUA savings realized by lower MUA cfm and temperature may become big building $ losses in a few years.

    Sent from my SM-G950U using Tapatalk

  6. #6
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    Thread Starter
    Quote Originally Posted by icy78 View Post
    It needs to be looked at by someone who can "see" the whole building picture. Mechanical as well.
    Small MUA savings realized by lower MUA cfm and temperature may become big building $ losses in a few years.

    Sent from my SM-G950U using Tapatalk
    Do you know where we should look for an HVAC expert that can look at the entire building?

    We have a mechanical maintenance company that maintains the MAU and other equipment. Should we have them do this, or would it be better to bring in somebody from a company that installs MAUs, or a company that manufactures MAUs?

  7. #7
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    Quote Originally Posted by nielkfj View Post
    I live in a small condo building.

    Myself and some of the other owners are interested in improving the energy efficiency of the building.

    One of the things we are considering is adjusting the temperature and/or
    air flow rate from a make-up air unit (MAU) that supplies air to the building hallways.

    With respect to this, the questions I have are:

    1) Other than the comfort level of the temperature in the hallways,
    are there any other factors that we should be considering?

    HUMIDITY CONTROL

    2) Is there a simple way to adjust the air flow rate from a MAU?

    __ AUTO ADJUST DAMPER would be standard on MAU.
    Damper would be controlled by providing ~ 0.05" W.C. Positive Pressure


    3) Are there any other common ways to make a standard MAU operate more energy efficiently?

    CO2 Controller may be an alternative in a few situations.

    _ Might wish to think about manually opening window during Clothes Air Dryer use.
    Control the TIMING AND AMOUNT of exhaust air from EACH Condo.

    ASHRAE STD. 62.2 - 2013
    ___ Understand & Use the INFILTRATION CREDIT _ _ from data provided by a BLOWER DOOR TEST

    For example,
    _ 30 CONDOS * ~ 40 CFM / CONDO = 1,200 CFM Total Continuous ( weekends )
    __________ 40 CFM Could be less than a Continuous flow rate.
    ______ … … No one home during the day _ _ Reduce exhaust air flow rate for upto 12 hours

    https://www.energy.gov/sites/prod/fi...ily_walker.pdf
    Last edited by dan sw fl; 11-29-2019 at 07:23 AM.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  8. #8
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    You need a Mechanical Engineer. There are several factors involved, Building code and Fire Codes. Residential building Common areas are Positive pressure. Hallways, Emergency stairs Etc. Air changes per hour requirements need to be meet!

  9. #9
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    Is the MAU using gas for fuel? And do each units have a gas fireplace? I have seen condos where the gas is on a common meter and during the winter, the fire places are on and drives up usage.
    UA Local 32 retired as of Jan 2020

  10. #10
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    Big capital expense, but might consider an air-to-air heat exchanger that takes all the exhaust air (bath vents) from the building in a common duct and transfers the recovered heat into the supply air. Supply air will be cooler than what you have now, but economy of operation is worth the look.. All the new hotels I've seen use these.

    As to efficiency of MAU, if it is a direct fired type, it is 100% efficient. Engineer is recommended in any case, one that has actually worked hands on in the field is preferable..
    “A dying culture invariably exhibits personal rudeness. Bad manners. Lack of consideration for others in minor matters. A loss of politeness, of gentle manners, is more significant than is a riot.”
    ― Robert A. Heinlein

  11. #11
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    double..
    “A dying culture invariably exhibits personal rudeness. Bad manners. Lack of consideration for others in minor matters. A loss of politeness, of gentle manners, is more significant than is a riot.”
    ― Robert A. Heinlein

  12. #12
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    IMO, you need a good tech, who can also think like a mechanical engineer.
    Or a good mechanical engineer, who has a tech who can make the ME's design work properly.

    Sent from my SM-G950U using Tapatalk

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  14. #13
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    Quote Originally Posted by Juan Madera View Post

    As to efficiency of MAU, if it is a direct fired type, it is 100% efficient.
    Ha, I was waiting for someone to say this! It don't get more efficient than 100%, well unless it's a heat pump, but I've gotten into some heated arguments about how it's impossible for heat pumps to defy the laws of physics, so I'm not going to go there.

    With that being said, I believe direct fired units are banned from areas where people sleep, so I'm guessing it has heat exchangers.

    Quote Originally Posted by nielkfj View Post
    I think we have pretty good positive pressure in our building. If I put my hand at the bottom of the entrance door to my apartment, I can feel air blowing lightly underneath the door from the hallway...
    This doesn't prove anything other than that your apartment is at more of a negative pressure than the hallway is. A better test would be to go down near the water heaters/boilers when they're not running and hold a match near the flue pipe and see which direction the flame goes (assuming that they're natural draft with no dampers), or go near an outside door to the building and do the same thing with the door slightly cracked.
    Last edited by ammoniadog; 11-29-2019 at 10:27 PM.
    If at First You Don't Succeed, Skydiving Is Not for You.

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