Carrier 58STA vs. 58CVA, is extra $ for variable speed blower, 2 stage worth it? - Page 2
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  1. #14
    Join Date
    Nov 2004
    Location
    SW FL
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    6,225
    Quote Originally Posted by Jreality View Post
    I doubt 110K is twice the size needed, given that my townhouse is over 3K square feet, if you include the finished basement.
    it may only be 175% of what is required IMO.! _unless your design temperature is << -1F.
    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
    Nov 2012
    Posts
    39
    There are days when the outside temp can get that cold around here.

  3. #16
    Join Date
    Nov 2004
    Location
    SW FL
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    6,225
    Quote Originally Posted by Jreality View Post
    My highest gas bill over the past 12 months was $169.76 for the billing month ending on Jan 20th 2012, and during the prior year, the highest was $220.50 for that same billing month (ending in Jan 20th, 2011). During the year before that, my highest bill was $285.92 for that same billing month (ending in Jan 20th, 2010). I'm in Northern NJ.
    Use of 1,000 therms per year correlates to ~60,000 BTU/HR Design Heat Loss for a climate with 5,200 Heating Degree Days

    ~ 60,000 BTU/Hr is reasonable for a 3,200 sq foot residence with R-30+ ceiling, R-11 walls, 320 square feet of windows with U 0.4

    Description: Fahrenheit-based heating degree days for a base temperature of 65F
    Station: Morristown Municipal, NJ, US (74.41W,40.80N)
    Station ID: KMMU

    Month starting
    .................. HDD N.Gas/mo.
    11/1/2009 -- 527 $135 4,697
    12/1/2009 -- 991 $254
    1/1/2010 -- 1116 $286 0.256
    2/1/2010 -- 925 $237
    3/1/2010 -- 607 $156
    4/1/2010 -- 346 $89 .......Annual
    5/1/2010 -- 185 $47 ---- $1,204
    6/1/2010 -- 59
    7/1/2010 -- 31
    8/1/2010 -- 46
    9/1/2010 -- 112
    10/1/2010 -- 366 $66 5,311
    11/1/2010 -- 667 $120
    12/1/2010 -- 1098 $197
    1/1/2011 -- 1231 $221 0.180
    2/1/2011 -- 941 $169
    3/1/2011 -- 784 $141
    4/1/2011 -- 410 $74 ........ Annual
    5/1/2011 -- 165 $30 ......... $1,016
    6/1/2011 -- 50
    7/1/2011 -- 19
    8/1/2011 -- 28
    9/1/2011 -- 77
    10/1/2011 -- 398 $69 5,868
    11/1/2011 -- 555 $97
    12/1/2011 -- 817 $142
    1/1/2012 -- 977 $170 0.174
    2/1/2012 -- 806 $140
    3/1/2012 -- 539 $94
    4/1/2012 -- 398 $69 ....... Annual
    5/1/2012 -- 140 $24 ___ $806
    6/1/2012 -- 73
    7/1/2012 -- 12
    8/1/2012 -- 47
    9/1/2012 -- 141
    10/1/2012 -- 334 ....... 4,839
    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

  4. #17
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,132
    If you think you need over 60k, fix the house instead of installing a beast of a furnace. Your comfort will be higher and your utility bills will be lower. It's better to reduce the heat loss rather than find a more efficient way to replace the lost heat.

  5. #18
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Quote Originally Posted by Jreality View Post
    My highest gas bill over the past 12 months was $169.76 for the billing month ending on Jan 20th 2012, and during the prior year, the highest was $220.50 for that same billing month (ending in Jan 20th, 2011). During the year before that, my highest bill was $285.92 for that same billing month (ending in Jan 20th, 2010). I'm in Northern NJ.
    If you run the numbers backwards, with a 80% furnace at @ $0.90/therm... that's 34,608 average useage per hour. The coldest month is usually on average about 50% average capacity give or take, so that's puts you around 60-70k BTU's required depending on water heating useage, your actual gas rates, etc.

    I love hte photo that was posted on another thread of someone's Carrier Infinity controller showing I think ti was 2F outdoor temeprature (below design conditions), and a 60k BTU furnace holding temp on medium stage in a 3300 sqft house on top of a windy hill in upstate New York. SO that home was only using 45k BTU's.

  6. #19
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Quote Originally Posted by dan sw fl View Post
    Use of 1,000 therms per year correlates to ~60,000 BTU/HR Design Heat Loss for a climate with 5,200 Heating Degree Days

    ~ 60,000 BTU/Hr is reasonable for a 3,200 sq foot residence with R-30+ ceiling, R-11 walls, 320 square feet of windows with U 0.4
    I think in reality you could be even lower. It's 3 story, and that's not a whole lot of window area for a home that size...although typical for newer homes. Again, my home has twice the windows, with higher U values, and lwoer wall R values, and 60-65k will heat the whole house no problem... but Manual J would put it a little higher.

    Infiltration is one of the tricky things to estimate.

    Heating really is easy. AC gets a little tricky because it's impacted so much more by quality of installation, airflow, latent loads, outdoor air temps, how clean the coils are, air leaks, solar heat gains and so on. Furnaces don't have much vairability.

  7. #20
    Join Date
    Nov 2012
    Posts
    39
    Let's say everything really is oversized....is the 2 stage going to help me or hurt me in that situation?

    I'm also still wondering if the Variable Speed is going to help me or hurt me in the summer with rooms upstairs (I'm on a 1 zone system) or is going to hurt me. I was just told that in the summer it will start out at 200cfm and ramp up to 1600cfm 'til the stat is satisfied and then ramp back down to 'til the blower shuts off. And, no they are not running the extra wiring, they say the furnace has a timer. I'm now wondering how long it takes for the fan to ramp up to the full 1600 in the summer...and if the process is slow will this make it worse or better for the upstairs rooms?

    Can the Carrier 58CVA be programmed by the installer to ramp up very quickly to 1600CFM (or even function as single speed for AC) or is would I be stuck with a ramp up process that is designed for heat? (again, they're not giving me a 2-stage stat or running the extra wiring).

  8. #21
    Join Date
    Jan 2009
    Location
    Keokuk, IA
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    5,520
    2nd stage will make a big improvement if it's oversized. If you only need 60k and install 110k, on 1st stage you'll get around 75k, so it will be a lot closer. IT will still only run <50% of the time most of the winter, but on the coldest days it will come close to running continously on low stage early in the morning.

  9. #22
    Join Date
    Nov 2012
    Posts
    39
    What about in the summer? There have been days when it is in the upper 90s outside, and my current system ran virtually continuously with the downstairs thermostat set at 75. There are rooms upstairs that can be 5 to 7 degrees warmer than downstairs during the day. Is the variable-speed blower with a slower ramp-up to full speed going to worsen the situation upstairs?

    I'd like to know more about how the ramp-up form slow to full blower speed on the 58 CVA will work in the summer when using a 13 seer unit and a single stage stat....

    how long does it take to reach full speed, and does the length of ramp-up vary?

    Could it be programmed to ramp up quickly to work more like a standard blower if I found it worsened the situation with rooms upstairs?

  10. #23
    Join Date
    Nov 2012
    Posts
    39
    This is what I was told in an email: "you set it for 1600 for ac it will begin at 200 cfm ramp up to the 1600 setting until the stat is satisfied then ramp back down till it shuts off.
    "

    That has me concerned, because it seems to me that running at the very slow speed for any length of time for 4 ton unit sounds like it would cause more harm then help, or does it only run at 200cfm for a few seconds and then gradually speed up? It would be nice to know the ramp-up processe. If I understood exactly how the ramp-up process works, it would be helpful.

    NOTE: I'm going with a 13 seer, which is a single speed AC so I need to make sure the VS model will work properly with it (and not worsen the situation with rooms upstairs)

  11. #24
    Join Date
    Nov 2012
    Posts
    39
    Okay they cleared it up....the fan runs at full speed when the compressor is running.

  12. #25
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    To improve cooling upstairs, you want the smallest AC possible to cool the entire home. Oversizing the AC will make any temperature imbalances worse, much worse. You also should consider a thermostat that measures humidity and than can slow the blower down to dehumidify better.

    When it's in the upper 90's in NJ, your above design temeprature and it should be running constantly and even falling behind a little. Nothing will fix inadequate ductwork. A perfectly sized unit should run for 8-10 hours straight at design conditions. The longer it runs the better. An AC system needs 8-10 minutes to equalize ("warm-up") just to reach maximum efficiency.

  13. #26
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    6,244
    The blower ramps up like pressing the accelerator on your car. Only take a few seconds to get to full speed.

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