Need HVAC advice

[Timelord]

I recently had a friend come to me for some engineering advice and I thought I’d pass along his problem to this forum to see what you all can suggest. My friend is a wine collector and he has constructed a wine cellar to store his collection. I’m no wine expert (MD 20/20 is my speed) but the question relates to HVAC for his cellar. He has constructed a 6’ X 6’ room with R60 in the walls and ceiling. It is sitting on a ground floor slab and we are located in Albuquerque. He tells me that the best way to store wine is at 55deg to 60 deg , minimizing all thermal swings. He tells me that the absolute temp is not as important as minimizing both the amplitude and number of thermal swings the wine sees. He has monitored the room and the temp is pretty stable, but here in the southwest the average temperature rises to high in the summer for the wine. He wants to add a small chiller or air conditioner to keep the temp from rising in the summer. I reasoned that cooling the air directly is not the way to go. I advised him to use the chiller to chill a large thermal sink fastened to the wall opposite the wine rack. The question is how to control the temperature. I think the way to go is to put the thermocouple for the controller in the thermal sink or even in the slab, but not in the air, to minimize any swings when he enters or leaves the cellar. Maybe even more than one temp probe and an intelligent controller. Any thoughts on a simpler way to accomplish his intent?


Timelord

 

[superheat]

Sounds like a good idea. I would put a thermostat in the room and a low temp limit on the circulating water. A small compressor would probably have the least temp swings.

 

[MintJulep]

The goal is to prevent temperature changes of the wine in the bottles.

How can energy get to the wine?

Conduction through the rack into the glass of the bottle and then convection into the wine.

Convection from the air to the glass of the bottle, conduction through the glass, then convection into the wine.

Radiation.

If the rack is wood or some other material with low coduction, and is at the same temperature as the bottle then conduction is essentially zero.

I'll assume that the light is off most of the time, and since the surface temperatures of the bottles and the interior walls should be about equal radiation should be very small.

That leaves convection from the air as the prime way the wine may get heated.

The change in temperature is a fucntion of the difference in temperature between the wine and the air and how long the delta T is maintained.

So it seems to me that directly cooling the air is actually a good way to go. Open the door, warm air goes in. Quickly cool the air to minimize the time that warm air is in contact with the bottles and there will be minimal change in the temperature of the wine.

A vestibule to limit the amount of warm air that could enter would also be effective.

 

[steam4]

Try this site:

http://www.wineracks.com

They have environmental control units for your application. There are probably other sites as well.

 

[pennpoint]

timelord
The concept you propose sounds nice and may be a fun project. But I am going with MintJulep with this one.
If an outside wall is available a small (thorugh the wall) window type air conditioner will be less expensive and easer to maintain. A timer/thermostat control system can be used to operate it during the warmer periods.

Please let us know you friends address so we can be there for the next tasting.

pennpoint

 

[cjw81]

Mintjulep explained pretty much the basics, I would add to this that the best way to control a fluid temp is to immerse the cooling control sensor in proplyene glycol in a container similar to the wine bottles that you are using. You see that when you open the door, the air temp will change rapidly, but the wine temp will have a delayed reaction. To get the fluid reaction, use a fluid for sensing the "true" temp. of the medium being controlled.If you react to the air medium, you will overreact the response time. We use this method for storing blood in hospitals, a bit more critical than wine, but not as satisfying.

 

[chicopee]

Cool the air per Mintjulep' rec. and control temp per CJW81's rec. I would add a plastic curtain at the entrance as you have w/ refrigerated coolers to minimize air exchange when you open the door.
As a estimated guess a 3000 to 6000btu/hr AC system s/b sufficient for cooling.

 

[jb48]

Cooling the air will work, but it requires an active control scheme and electric power. A power outage on a hot day could lead to a lot of ruined wine, unless of course he calls all his friends over to drink it up before it is subject to the high temperature.

The best way to eliminate temperature swings is to use a passive approach, i.e. lots of thermal mass in the enclosure. Its probably too late now, but I would construct such a room, below ground if possible, or with heavy masonry walls, insulated on the exterior side. This is the reason that wineries usually store their wines in caves or cellars. There is also a passive solar concept which uses a wall made of water filled 50 gal. drums. I believe its called a Trumble wall.

 

[Teto]

timelord,
Many years ago I proposed doing the same thing (using an HVAC unit rather than a commercial refrigeration unit). Although it will work the problem is that to achieve 60 degree air, the refrigeration apparatus will go below freezing at the coil surface. HVAC units are not made for this type of service. A refrigeration unit for this type of service will have a timer that wiil force the compressor off to thaw the ice off the coil. An HVAC unit is cheaper but should have a timer installed. I realize this has nothing to do with the elimination of temperature swings, just thought I'd provide other factors to consider. Also I make my own wine in Albuquerque so I sympathize with your friend.
teto

 

[ClydeMule]

I have been working on designing a packaged system for this kind of stuff. We have made a few already. WE have used chiller water in a small coil to help keep a constant setpoint. Little more expensive, a little less efficient, but much better control.

One of our first thoughts was to do what you had said, cool the wine bottles or racks directly. Unfortunetely this becomes impractical, doesn't cool as efficently as you might think.

Another reason cooling the air winds up being better is that you also have to maintain the proper humidity.

THe best advice given so far is to have a well insulated room with a good vapor barrier.

Happy drinking.

Clyde