Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Wine Room Evaporator / Condenser Match Question - Need Guidance

BigRob
BigRob Member Posts: 322
Hi all! Hope you are enjoying your Summer.

I'm in the final stages of planning a wine room refrigeration system. The previous evaporator coil sprung a leak and the whole system is pretty old. I've been wanting to try Zoomlock fittings, so I bought a Zoomlock hand crimping tool from Amazon to give it a go. I'll also add a fan control and the new condenser will have a receiver. Will post pics and impressions when complete.

The wine room is pretty small and adjacent to the living room, so I'm going to use a gravity coil I found with a suction temp of 38F. The room temperature will be 55F. Based on insulation and wine room construction, the evaporator heat load is around 1500 to 2000 BTU/hr, so with compression heat I am shooting for a condenser of about 2500 btu/hr.

Which leads me to my questions..

1) Condenser operating data is spec'd at different evaporating operating temperatures: 25 ,30 ,40, etc. This is the evaporator suction temperature, correct?

2) Condenser ambient temperatures are listed at 90, 100, etc, and capacity obviously increases when the condenser in in a cooler environment. My next question is, if I need 1850 btu/hr (16hr recommended run time) and the condenser output changes based on ambient temperature, at what operating point do I select to specify the correct condenser? The gravity coil manufacturer stresses that the condenser capacity should not be larger than the gravity coil capacity, which is 2035btu/hr at 38F suction / 17F TD. Even some 1/5hp units might be close to exceeding 1850btu/hr at 70F ambient, but this information is not given. What is the convention when matching evaporators and condensers? Do I extrapolate to the city average temperature for ambient temperature and plan on longer run times for hot days? I am missing something and need some guidance.

Thanks, Ched

Comments

  • Red or white? French or domestic? What's your address?
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • BigRob
    BigRob Member Posts: 322
    Red. French & fruity. Also domestic - so many great options, everywhere now.

    We are in Granite Bay, CA.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,452
    The equipment selection is base on a lot of variables (as you have found out) Heat output from the condenser is about 1.3 x cooling load but condensers are rated by how much cooling they produce. So a 2 ton condenser should give you about 24,000 btu/ hr cooling load the condenser will reject about 24000 x 1.3 or 31,200 btu/hr.

    I would stick to what the manufacture of the coil recommends.

    This is what happens @2035 btu gravity coil lets say you use a condenser rated at 1850 btu. The two find a balance between them the suction pressure will be a couple of lbs higher and the run time may be slightly longer but the difference in operation will hardly be noticed. And yes pick the outdoor condenser based on your average high outdoor temp...doesn't have to be the highest temp you ever get. You should be able to get charts from the condenser manufacturer to aid in selection
  • HVACNUT
    HVACNUT Member Posts: 5,803
    Any way to install the condenser inside an equipment room?
  • BigRob
    BigRob Member Posts: 322
    HVACNUT said:

    Any way to install the condenser inside an equipment room?

    It would be a much bigger job.
  • BigRob
    BigRob Member Posts: 322
    Will the fan cut control keep the head pressure up in winter days? Not sure how to calculate this.

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,452
    @BigRob , yes if the condenser operates in a cold climate you need a fan cycler or condenser bypass controls and a receiver Sporlan makes those controls but you can usually by the condenser with the controls you need
  • pecmsg
    pecmsg Member Posts: 4,775
    Fan cycling works but wears out the motor and causes problems with the x-valve. A head master is much better method.
    Solid_Fuel_Man
  • BigRob
    BigRob Member Posts: 322
    Head master control looks pretty cool. I will have to look into calculating the refrigerant volume to see if a receiver that comes with a typical 1/5hp condenser will be large enough. Let me know if you have any top of the mind thoughts.

    Also, what are your thoughts on variable fan speed head control schemes?
  • pecmsg
    pecmsg Member Posts: 4,775
    Smallest system factory built I know of is 1/2-HP
    Speed drives are better then on off.

    1/5-HP you’ll have to build it.
  • BigRob
    BigRob Member Posts: 322
    No problem building it. You think a 1/5hp condenser comes with a large enough receiver or too many variables to know for sure?
  • pecmsg
    pecmsg Member Posts: 4,775
    What size box
    Insulation good
    How long of a line set.

    Humidity used to be a requirement but today all corks are synthetic do a non issue.

    There are several nice systems available depending on how deep there pockets are.
  • BigRob
    BigRob Member Posts: 322
    25ft of lineset. 2x4 wall with fiberglass batt and foil faced 1/2” foam between the studs and wine room interior drywall.

    It’s more of a wine closet - about 1800 btu/day on warm days. I gamed the Calcs and that is about right.
  • pecmsg
    pecmsg Member Posts: 4,775
    Vapor barrier on the inside or outside of the box?
  • BigRob
    BigRob Member Posts: 322
    Inside
  • pecmsg
    pecmsg Member Posts: 4,775
    Vapor barriers on refrigeration go on the outside.

    You want to prevent the moisture from condensing in the insulation.
  • BigRob
    BigRob Member Posts: 322
    Let me think, the foil is on the outside of the 1/2" foam board. The foam board is inside of the stud, so the foil and wood of the stud are touching. The previous system did not cause and issues so I think it is fine, either by luck or design.

    Stackup is like this: Outside room-> outside drywall->stud/fiberglass->foil->1/2"foam board->drywall in wine room
  • pecmsg
    pecmsg Member Posts: 4,775
    Warm Moist air migrates to a cool dry environment!
  • BigRob
    BigRob Member Posts: 322
    Hopefully there is something I am not seeing. I could only see through the hole for the thermostat into the wall cavity.
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
    We are only talking a room temp of 55F, I'd assume the dewpoint of the indoor environment will be below 55F. This isn't a walk in cooler.

    I'll bet the 1/2" foam would keep the dewpoint at bay.
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • BigRob
    BigRob Member Posts: 322

    We are only talking a room temp of 55F, I'd assume the dewpoint of the indoor environment will be below 55F. This isn't a walk in cooler.



    I'll bet the 1/2" foam would keep the dewpoint at bay.

    There is no evidence of water damage anywhere after 10 years, so it should be fine.
  • BigRob
    BigRob Member Posts: 322
    Ok, I think I am getting closer to understanding what to do. I have one question about evaporator sizing and how to set the correct evaporator temperature. Please correct me if you sense I have made some incorrect assumptions.

    For a heat load of 1800btu/hr and box temp of 55F and 38F suction temp, I look at the condenser charts and pick the condenser with a cooling capacity close to 1800btu/hr around 38F evaporating, so call it 40F evaporating temp. I get this. So now I know my condenser. For sake of argument, lets say at 90F ambient the condensing temp is 113F.

    From here I get fuzzy. I see most evaporator units are rated at 10F TD. I also see that capacity increases with higher TD. How do I select an evaporator considering I want a 17F TD?

    Also, how do I set the suction temperature during commissioning? I see that TXV's set superheat and let temperature float. I have also been reading a bit about EPR's.
  • pecmsg
    pecmsg Member Posts: 4,775
    Your evaporating temp will be 15 - 20* F lower depending on the temperature drop. If you insist on s gravity coil figure 20 - 49* drop.
  • BigRob
    BigRob Member Posts: 322
    So, does the evaporator rating scale linearly with TD? For example, an evaporator rated and 10,000 btu/hr at 10F TD is 1000btu/TD/hr, so at 17F TD the same evaporator is rated at 17,000 btu/hr?
  • pecmsg
    pecmsg Member Posts: 4,775
    The larger the TD the lower the pressure so the less BTU capacity for the given refrigerant!
  • BigRob
    BigRob Member Posts: 322
    Ok. I'm trying to understand how to select an evaporator. The industry uses a 10F TD as the nominal rating condition for evaporator units. I would like to run 17F TD (for wine) with a 1800btu/hr wine room load at 38F SST, so the wine room ambient is 55F. I believe I need to scale the evaporator rating by some factor. I guess for a given fan speed, to increase the TD you would decrease the coil size, and to decrease the TD you would reduce the coil size. This makes sense.

    So, it would be: Effective 17F TD coil rating = (10/17) * (10F TD coil rating). So 0.588 * 1800btu/hr is 1059btu/hr. So I would select a 10F TD rated coil of capacity around 1058btu/hr to run with my 1800btu/hr, 40F SST @ 90F ambient condenser.

    Does this seem right?