Wine Room Evaporator / Condenser Match Question - Need Guidance

BigRob

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

Alan (California Radiant) Forbes

Red or white? French or domestic? What's your address?

BigRob

Red. French & fruity. Also domestic - so many great options, everywhere now.

We are in Granite Bay, CA.

EBEBRATT-Ed

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

Any way to install the condenser inside an equipment room?

BigRob

HVACNUT said:

Any way to install the condenser inside an equipment room?

It would be a much bigger job.

BigRob

Will the fan cut control keep the head pressure up in winter days? Not sure how to calculate this.

EBEBRATT-Ed

@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

Fan cycling works but wears out the motor and causes problems with the x-valve. A head master is much better method.

BigRob

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

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

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

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

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

Vapor barrier on the inside or outside of the box?

BigRob

Inside

pecmsg

Vapor barriers on refrigeration go on the outside.

You want to prevent the moisture from condensing in the insulation.

BigRob

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

Warm Moist air migrates to a cool dry environment!

BigRob

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

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.

BigRob

Solid_Fuel_Man said:

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

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

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

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

The larger the TD the lower the pressure so the less BTU capacity for the given refrigerant!

BigRob

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?