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Recent content by GMcD

  1. GMcD

    Do we need to notice the failed contractors

    In my opinion, yes, it's the professional thing to do. You may have to work with some of those contractors on other projects and a courtesy note saying that you thank them for their effort, but weren't successful, to be sent out as soon as possible after you've selected your contractor buys a...
  2. GMcD

    100% Outside Air System

    As Drazen said plus look at whether you are exhausting point source equipment and "source of heat" exhausts to get the total actual "cooling" load that needs to be applied for worker comfort.
  3. GMcD

    Ventilation for food processing plant

    For food processing plants you may find that the amount of point source exhaust and process equipment exhaust will define the amount of fresh air/make-up air required. Consider a heat recovery system if you are in a cold climate. There will also be refrigerant detection and alarming...
  4. GMcD

    Building Pressure Relief

    "Codes" are a Minimum Safety Standard - there is a lot that is not in any "Code" that the design engineer has to actually do some real design to accomplish a successful building HVAC system. The "Codes" are not supposed to be a design guide/checklist - the Code is the minimum bottom line that...
  5. GMcD

    Ceiling Radiant cooling/Heating

    What BronYrAur said- from what you are asking, it seems like you are trying to rationalize the use of the heat and cool source, and then try to make the radiant system work based on your sources of heating and cooling. I've been designing and operating radiant systems (slabs, panels, floors and...
  6. GMcD

    Direct fired MUA

    Client just saved a bagful of money (he thinks) buying cheap direct fired MUA's. Now the reality of Code Compliance will require spending probably triple what the Client saved, on interlocks and new controls, plus your time in proving to the AHJ that the localized direct fired air quantity is...
  7. GMcD

    Estimating Glycol Amount in Chiller/FCU System

    Or you could just drain down the entire system and re-fill it with a known, mixed 30% propylene glycol mixture till it's full again. Or just keep adding and draining off fluid till testing indicates a 30% mix. Or do some real engineering and do a proper estimate and calculation to start, in...
  8. GMcD

    VRF Systems in Mechanical Rooms and ASHRAE 15-2013

    I'm not sure why an Owner/developer can dictate to a professional engineer what system to use, but if you are OK with the potential risks and possible benefits, then fine. I have found that VRF systems tend to be a system where the installer/supplier can then work it into a nice service...
  9. GMcD

    VRF Systems in Mechanical Rooms and ASHRAE 15-2013

    It sounds a little like you are trying to pound a square peg in a round hole. VRF systems and residential occupancies are risky at best, and I would suggest that a well designed and operated conventional four-pipe fan-coil system would work just as well, on a budget, and have a lot less risk...
  10. GMcD

    GMCD contact Info

    GMcD contact info geoffmcdonell@hotmail.com also on LinkedIn
  11. GMcD

    Flexible air duct – maximum length

    Good practice is to use less than 2 meters or less than 6 feet. The issue is the high air friction as well as supporting the flex duct to prevent kinks and sharp bends.
  12. GMcD

    How often should an engineer visit a job site?

    There are also local PE and P.Eng. Association requirements for "good practice" (that will hold up in court) - for example - in British Columbia, APEGBC REQUIRES the engineer of record to make site reviews at his discretion, or if the site reviews are delegated, it must be at the EOR's direct...
  13. GMcD

    Minimum outside air on VAV

    There was similar information discussed and referenced in this discussion: http://www.eng-tips.com/viewthread.cfm?qid=408480
  14. GMcD

    Add heat for ground souce heat pumps?

    It sounds like you have water to air type heat pump units? In that case, yes, you'll likely have to add heat to the condenser (source) water loop if that is falling too low as the heat pumps are extracting heat. I don't think the fact that the condenser water can sit in the loop without...
  15. GMcD

    Add heat for ground souce heat pumps?

    What Drazen said. Here in Canada there are a number of early adopters' efforts that resulted in permafrost being formed due to value engineering the ground loops and just plain poor ground loop/borehole designs. There is also a way to recharge the ground using solar thermal panels depending on...
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