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  1. #14
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    5,998

    Thumbs up ASHRAE 62.2

    Quote Originally Posted by beenthere View Post
    I don't recall ASHRAE suggesting an air change in 5 to 6 hours.

    There formula for calculating min air change doesn't come out to that.
    4 to 5 hours for a whole house air change seems to be
    close to ASHRAE 62.2 recommendations,

    2,400 sq foot residence = ~ 20,000 cubic feet

    4 hours ... 5,000 cubic feet per hour ... ~ 85 CFM.
    5 hours ... 4,000 cubic feet per hour ... ~ 67 CFM
    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

  2. #15
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,808
    Quote Originally Posted by dan sw fl View Post
    4 to 5 hours for a whole house air change seems to be
    close to ASHRAE 62.2 recommendations,

    2,400 sq foot residence = ~ 20,000 cubic feet

    4 hours ... 5,000 cubic feet per hour ... ~ 85 CFM.
    5 hours ... 4,000 cubic feet per hour ... ~ 67 CFM
    Only when it has a lot of bedrooms.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  3. #16
    Join Date
    Feb 2011
    Location
    Lufkin, TX
    Posts
    24
    Well we have 5 bedrooms

    Please feel free to ask any and all questions that come into play. If this were a website, I'd be able to offer tons of advice.

    That's why I'm coming to you pros to ask questions.

    The second AC guy we talked to is a contractor for one of "the biggest and best" builders in our area and supposedly does a lot of foam houses. He is doing the HVAC for a large house being built a few miles from us by that builder with spray foam.

    He's also the one who said we shouldn't need a heat pump or fresh air intake.

    I know that a high price doesn't mean high quality and that a lower price doesn't mean that they will do a bad job. In the web design business (my trade), I know of many companies who do half as good of a job as I would for double the price.

  4. #17
    Join Date
    Feb 2011
    Location
    Lufkin, TX
    Posts
    24
    I read over my previous post and hope I didn't sound arrogant.

    I'm just concerned that we will choose the wrong contractor and want to make sure that I know what to look for and what questions to ask.

  5. #18
    Join Date
    Oct 2010
    Location
    Houston, Tx
    Posts
    2,093
    Houston does not have very many heat pumps, I know of one that I have been involved with the installation at my sister's house in Katy. It will lower your HEATING bill as refrigerant heat is much less expensive versus electric (not sure how much less than gas it is but you aren't using gas with refrigerant heat, it's the same refrigerant used for cooling so you are not paying for gas) and from what I understand that's the main use of a heat pump where you run heat a lot out of the year. In Texas, Houston that I am certain of anyways, cooling is 90% of the time so the extra 1k to 2k to 3k for a heat pump is not worth the cost as you will more than likely never get that money back as we don't use heat anywhere near enough to attempt to really save on it.

    That's the only reason I can come up with why a heat pump is not recommended for your location and not something I would off the bat neglect the company(s) that rejected them over as they apparently just didn't give you enough info on why not a heat pump which basicly boils (inside hvac joke, pun intended, ha ha) down to being a waste of money on your part. Now if you travel up north to the states that use heat 50% to 60% or more of the year, they're everywhere or so I've heard, and rightfully so.

    I'm not the expert these other guys are, only giving you my opinion.

  6. #19
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    5,998

    Thumbs up Residential Ventilation rate = one or two small bath fan

    Quote Originally Posted by beenthere View Post
    Only when it has a lot of bedrooms.
    2,400 sq. feet * 8 = 19,200 cubic feet
    6 hours ... 3,200 cubic feet per hour ... 53.33 CFM

    Use 0.01 Floor Area + 7.5 * ( # of bedrooms +1)

    .01* 2,400 sq ft + 7.5 * ( 3 +1 ) =
    24 + 30 = 54 CFM Continuous

    53.33 = 54 CFM .. looks pretty close to me for 8 foot ceilings.
    Of course, many residences have greater ceiling heights.
    9 foot ceiling, one needs ~12% more,
    or 60 cfm per TBs rule-of-thumb ( 6 hours)

    Take your pick for these continuous ventilation rates
    or use greater ( ~ 2 x) for Intermittent ventilation.

    Have timers ( 5 to 15 hours) on bath room exhaust fans come into being a regular practice?
    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

  7. #20
    Join Date
    Jul 2006
    Posts
    1,091
    Quote Originally Posted by dan sw fl View Post
    Have timers ( 5 to 15 hours) on bath room exhaust fans come into being a regular practice?
    I prefer the supply method, your house is not in a vacuum sucking in fresh air from every crack and crevice. That just doesn't seem fresh to me.

    Honeywell has a neat little damper and timer
    http://www.forwardthinking.honeywell...ll/68_0282.pdf

  8. #21
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,065
    Keep in mind that we are splitting hairs with all of the discussion of percise air flow. On a cold day with +7 mph wind most home are getting an air change in 4-5 hours. Operating an ERV directly adds to the natural ventilation. This quickly leads to over ventilating. Very little payback in that. Operating make-up ventilation reduces the infiltration by about 50% of the make-up rate. During calm moderate weather, there is no cost reduction with ERV. Also limiting the ventilation to the time when occupied also reduces the cost of ventilation. In most climates and most homes, ERVs have a very poor payback plus expensive and complicated.
    The most practical method of control of fresh air is an occupancy timer that provide fresh air when the home routinely occupied. As the home becomes to dry during cold weather the fresh air ventilation can be cut back. Ideally using a CO2 controller eliminates fresh air ventilation when the home is unoccupied or there is enough natural ventilation to eliminate the need for fresh air. ASHRAE suggest 7 cfm per max design occpants plus 1 cfm per 100 sqft. of floor space as a minimum. Also in multi occupants space 15 cfm per is suggested. Systems should be adjustable with volume and time. Also maintain <50%RH is important for health and comfort.
    Certainly an ERV is a good energy conserving device provided the space needs the fresh air when there is heat/moisture exchange for enough hours per yeat to pay for the investment and maintaince. ERVs do not eliminate the need for supplemental dehumidification or make-up air for exhaust appliances. Most are unable to afford both ERV and dehumidifier. The ventilating dehumidifier is the sensible starting point for those on a budget.
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  9. #22
    Join Date
    Feb 2011
    Location
    Lufkin, TX
    Posts
    24
    Quote Originally Posted by dan sw fl View Post
    2,400 sq. feet * 8 = 19,200 cubic feet
    53.33 = 54 CFM .. looks pretty close to me for 8 foot ceilings.
    Of course, many residences have greater ceiling heights.
    9 foot ceiling, one needs ~12% more,
    Our ceilings are 8 foot with three different areas having recessed (tray) ceilings that make them 9 foot.

  10. #23
    Join Date
    Feb 2011
    Location
    Lufkin, TX
    Posts
    24
    Number of occupants for the house is 5 and most of the time there is someone at home.

  11. #24
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,808
    Quote Originally Posted by dan sw fl View Post
    2,400 sq. feet * 8 = 19,200 cubic feet
    6 hours ... 3,200 cubic feet per hour ... 53.33 CFM

    Use 0.01 Floor Area + 7.5 * ( # of bedrooms +1)

    .01* 2,400 sq ft + 7.5 * ( 3 +1 ) =
    24 + 30 = 54 CFM Continuous

    53.33 = 54 CFM .. looks pretty close to me for 8 foot ceilings.
    Of course, many residences have greater ceiling heights.
    9 foot ceiling, one needs ~12% more,
    or 60 cfm per TBs rule-of-thumb ( 6 hours)

    Take your pick for these continuous ventilation rates
    or use greater ( ~ 2 x) for Intermittent ventilation.

    Have timers ( 5 to 15 hours) on bath room exhaust fans come into being a regular practice?
    Not in my area they haven't, at least not yet.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  12. #25
    Join Date
    Feb 2011
    Location
    Lufkin, TX
    Posts
    24
    Talked with a local company today. Feedback is welcome.

    This was all done over the phone and he said he would have to sit down with us and go over things more in detail.

    I told him our scenario and here is a summary of what he said:

    He told me up front that he was estimating the size of the unit and would have to use his software (O'brian is what he said he used I think) to get the actual unit size. He said that he could give us an actual unit size based on our blue prints. Is that the best way?

    He recommended doing some sort of report using an Energy firm out of the Dallas area.

    Does the main trunk line in 1.5" duct board and then uses the flex duct on the short runs.

    4 ton unit; 2 stages; he said the unit is able to remove humidity; thermostat control can be set to do humidity control; VS blower; recommends ERV; recommends heat pump

    2 configured units that he would recommend

    Lennox
    XP21048-230
    icomfort thermostat
    CBX40UHV-060
    16.2 SEER Rating

    XP16-048
    even heat on heat strips
    CBX32MV-060-230

  13. #26
    Join Date
    Nov 2010
    Location
    Schertz, Texas
    Posts
    5

    Heat Pumps are still worth the investment in Texas

    I work for an electric coop in the south-central part of Texas, dealing with energy efficiency. I've even been to Lufkin a few times on my way around the piney woods areas. Even with our fewer months of heating, and Roadhouse is right, the only way to justify any other form of heating other than a heat pump is to consider natural gas. If your contractor intends to use "strip" heating, don't consider it. My experience with our member's bills says that the heat pump cost versus a regular AC will pay itself back in a few years. This year we had at least 3 solid months of heating, and last year was definitely colder and longer. You're looking at a possible couple hundred bucks a month difference on those really cold months in the bills for those with heat pumps and without one. If you're planning on being in the house longer than 5 years, go with a heat pump and make sure they lock out your auxiliary heat down to the balance point on your system.

    I'm also not an HVAC expert, and this is just my opinion and experience working with an electric utility. And you came to the right place with these guys on these forums. After dealing with energy efficiency from this side, it's nice to hear from HVAC guys that want to see it sized right and dehumidify correctly. That's not always so usual in Texas these days.

    Foam is great. Quick advice: When you foam, especially with metal framing, make sure that "thermal bridging" can't occur between the framing members to an unfoamed portion. You probably already know that, but just in case...

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