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  1. #1
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    Jun 2005
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    Arrow Low Cost Fixes for North Country Heating & Cooling Costly Airflow Problems

    Any good Tech should already know what I am going to illustrate here; this is for Homeowners & any who can use the least costly way to deal with this too common a problem in the cold North Country.

    We are moving into the cooling season; however, any changes in equipment should consider how every component matches with optimal airflow efficiencies.

    My lowest cost solution to the cold climate oversized Oil furnace with a small tonnage A/C evaporator coil which requires nearly half the airflow as heating:

    I ran a check on my late brother’s home & the summer cooling heatload is about 14,000-BTUH.

    The original scenario, had much less airflow than required for 1.5T cooling; its 2-T A-Coil wouldn’t flow 1150-cfm for heating

    I did a lot of other figuring; 45,000-BTUH output should heat that small single story home.

    However, with the 140,000-BTUH input, 112,000 output Oil furnace installed; the nozzle size can be dropped from one gal an hour (we’ll use 139,000-BTUH input) to .75 @100-psi, the BTUH drops to 103,500 input, this furnace tested at .74% efficiency; *103,000 = 76,590-BTUH.

    Using a 90F heating temperature rise, which Thermo Pride can stand; (90*1.06 here) 76,590 / 95.4F is 803-cfm.

    Therefore, the 2-Ton A-Coil will handle the CFM; mounted +6 inches above the furnace, it has the flow capacity to work okay in both heating & cooling modes.

    With a third HP belt-drive motor, you could simply adjust the RPM down by turning the adjustable motor pulley out enough to get to 700 or 600-CFM for the 1.5-Ton A/C.

    The other solution is to install a multiple speed direct drive motor with the fan relay energizing the cooling speed tap.

    This rather common situation in cold climates seems not to be properly addressed my Techs, & the HO does not know why things don't work well.

    We should all work to improve efficient use of high cost energy ... so America & everyone wins.

  2. #2
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    The best option is to not grossly oversize the furnace like that in the first place.

    Doesn't putting in a smaller nozzel screw up the fuel to air ratio and reduce combustion efficiency?

    Doesn't there have to be a sufficient volume of exhaust moving through the heat exchanger for efficient heat transfer?

    Is oil heat still common in your area?
    General public's attitude towards our energy predicament: "I reject the reality of finite resource depletion and substitute it with my own; energy is infinite, we just need an alternative storage medium to run the cars on. The economy can grow indefinitely - we just need to "green" everything! Technology is energy! Peak what?"

  3. #3
    Join Date
    Sep 2002
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    Northeast Ohio
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    4,842
    Example: DMO BCL120 is factory rated for a low firing rate of .65 to max rate of 1.00 Four speed direct drive blower rated for up to 4 ton (1600) cooling. ECM is an option as well now so as long as you pay attention as Darrel has pointed out, acceptable parameters can be met.
    A good HVAC tech knows how, an educated HVAC tech knows why!

    DEM


  4. #4
    Join Date
    Jun 2005
    Location
    SW Wisconsin
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    Quote Originally Posted by amd View Post
    The best option is to not grossly oversize the furnace like that in the first place.
    Reply: these are existing old oversized Oil furnaces with small A/C or heat pumps added to them.

    Doesn't putting in a smaller nozzle screw up the fuel to air ratio and reduce combustion efficiency?
    Reply: The fuel to air ratio would have to be readjusted.

    Doesn't there have to be a sufficient volume of exhaust moving through the heat exchanger for efficient heat transfer?
    Reply: as a rule, yes; depends on how the mfg'er rates them. The venting system (chimney, etc.) would have to be sized to handle the lower BTUH to establish or make sure draft was going to be ample.

    Is oil heat still common in your area?
    Oil heat is in all the rural areas along with propane, most larger towns in this area now have natural gas. This is where I retired & there are a lot of fuel oil furnaces around here that are horrible mismatches.

    Oil, even per Therm units (100,000 BTUs), compared to natural gas, is high $ energy.

    Heaterman's example illustrates a broad application design that would be useful in cold Oil country.

    Of course, with new systems change-outs, if both heating & cooling are sized right, in my climate area the airflow CFM will be fairly close & no major problem.

    Home energy audits with some retrofitting, followed by an accurate manual J & sizing of all equipment to the heat-loss/gain loads should result in happier comfortable customers.

    Thanks for the input; I wasn't expecting any responses; however, resolving this problem is extremely important to our customers as serious damage can accrue to compressors & heat exchangers, etc., plus discomfort & very high utility bills.

  5. #5
    Join Date
    Jun 2005
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    SW Wisconsin
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    Why HVAC Systems are Less Efficient... By Rob 'Doc' Falke

    Quote Originally Posted by heaterman View Post
    Example: DMO BCL120 is factory rated for a low firing rate of .65 to max rate of 1.00 Four speed direct drive blower rated for up to 4 ton (1600) cooling. ECM is an option as well now so as long as you pay attention as Darrel has pointed out, acceptable parameters can be met.
    Why duct sizing, RA grille sizing, Filter rack sizing & proper airflow are so important.

    Sealing ducts is only part of the equation...

    Another great article on Government Energy program paying for what they're not getting.
    Real-Time Operating Delivered Performance is what counts, not speculations...

    Why HVAC Systems are Less Efficient than You May Think

    May 4, 2011 2:45 PM, By Rob 'Doc' Falke

    http://contractingbusiness.com/colum...fficiency0504/

    While sealing the duct systems is highly incentivized, it’s assumed, and has been for decades, that tight ducts alone are a solution. Once again, as shown by the average system static pressure of .86-in. and the average delivered airflow of 261 CFM per ton when the ducts were sealed, it was simply assumed that the ducts were sized correctly.

    When ducts are undersized by 25%, which most systems in the US are, simply sealing them is a recipe for disaster. Often the leaking return duct is the only thing that’s keeping the cooling coil from becoming clogged with ice or the high limit switch from continually shutting down the system.

    The result: The current energy efficiency program accepted a duct tightness test confirming only the lack of leakage as evidence the system was working. The program did not include live system measurements that would have verified the fan rated pressure and the delivered airflow to the space that would’ve easily confirmed the system was not operating within the manufacturer’s specifications.
    Last edited by udarrell; 05-04-2011 at 07:16 PM. Reason: Govt Energy programs - A quote from Falke's article

  6. #6
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    Jun 2005
    Location
    SW Wisconsin
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    Arrow Hopefully working Link To Rob 'Doc' Falke's Article...

    Quote Originally Posted by udarrell View Post
    Why duct sizing, RA grille sizing, Filter rack sizing & proper airflow are so important.

    Sealing ducts is only part of the equation...

    Another great article on Government Energy program paying for what they're not getting.
    Real-Time Operating Delivered Performance is what counts, not speculations...

    Why HVAC Systems are Less Efficient than You May Think

    May 4, 2011 2:45 PM, By Rob 'Doc' Falke

    http://link.contractingbusiness.com/...VSpWIc7C7xs=41 This link should work
    Hopefully, link will work:
    http://link.contractingbusiness.com/...VSpWIc7C7xs=41

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