Building a wine cabinet

I want to build a stand-alone wine cabinet with interior dimensions roughly 2' x 2' x 6' high (.6m x .6m x 1.8m).

I did a search of the threads on this site but did not come across anything on wine cabinets/cellars.

For construction of the basic cabinet, I'm thinking of using 2'x4's, R-13 insulation, plastic vapour barrier and either galvanized steel or sealed, moisture resistant MDF. One of the objectives in building a wine cabinet is to avoid vibration. MDF is frequently used for stereo speakers because it is accoustically dead. My thinking is that MDF, if the problem of humidity/moisture can be addressed, might also be suitable for a wine cabinet.

I would like to maintain a temperature of about 12 to 15 degrees Celsius/54 to 59 degrees Fahrenheit. Commericial wine cabinets tend to be either true refrigerators or cabinets containing what are essentially small air conditioning units. I would be interested to know what the difference is, and what kind of unit would be suitable for this application. I have also come across one unit, made by Dometic/Electrolux, that apparently does not use a compressor, although it is not clear to me how it works (http://www.silentcellar.com/technical.htm).

Are there practical ways to isolate vibration from a compressor from the rest of a cabinet, or at least to dampen it?

I should add that I have no problem with hiring a refrigeration professional in my area to provide advice on this. At the moment, I'd just like to get a sense of what the issues are and what I need to think about.

I'd also be curious to know whether I can just buy a second-hand refrigerator, tweak the thermostat to get higher than usual fridge temperatures and somehow dampen vibration.

Comments greatly appreciated.

Hi Rory,

Aside from the desired temperature for your wine storage, the other design criterian is humidity. If you use a refrigerator refrigeration system (low temp) you will have very low humidity and dry your corks out.

I suggest get the prepackage wine refrigeration unit (which is designed to maintain proper hunmidity) for your application.

Rory

The link you gave shows an "Absorbtion Cooler" which is compressor free and works on a different principle to the normal "vapour compression cycle" refrigerators that are more common.

You will be hard pressed to build one of these units as specialist tools are required. Even your local refrigeration technician would struggle as they are specialist units.

As Herefishy says, you would be better off going for the purpose made cabinet. Are you looking for long term storeage for ageing purposes or do you require a wine cooler? I like a drop of the vine most nights!

Frank

Hi herefishy,

Thanks for your comments.

My sense is that the manufacturers of prepackaged units do little more than say that their units will maintain humidity at somewhere between 50% and 80%. They are pretty opaque about how they do this, but it is in any event a rather borad range. Manufacturers who make fairly clear claims about humidity also charge an arm and a let for their units. For example, Sub-Zero wants about US$5000 for a unit that will store 140 bottles.

I think that I can maintain outside humidity at 55% - 75%. If I open the cabinet fairly regularly, which I plan to do, and perhaps put a small pan of water in the bottom of the cabinet, I would have thought that it would be possible to keep humidity over 55%, which should be fine for the corks.

Frank,

I'm interested in ageing more than short-term storage, for which my refrigerator is fine.

So much for absorption coolers. I'm told that the manufacturers of the prepackaged units all use pretty much the same off the shelf compressors. The rest would seem to be mostly cabinet, which is something I have experience constructing.

Let me put the question differently. If you refrigeration experts wanted to build a wine cabinet of the dimensions I've suggested, or perhaps a bit wider, how would you go about doing it?

Further on humidiity, I just came across Mr. Lloyd's article on the homepage about moisture removal and addition. Interesting.

You really don't want to keep 75% humidity in your house, do you? Anything over 60% can give you mold problems. 50%RH is ideal, and going over that is not necessary.

Let's say you keep your house at 75F with 50%RH. When that air drops to 56F, it's RH will be about 95% with a dewpoint of 54F. This means that any surface in the cooler whose temperature is below 54F will form condensation.

Of course, the only surface in there which is below 54F is the cooling coil. This coil will remove humidity from the air. How much it dehumidifies the air depends upon its temperature. The colder the coil, the more it dehumidifies. But it needs to be cold enough to maintain the temperature inside the cooler.

If the coil temperature is not allowed to drop below 42F, assuming the cooler temperature is 56F, then the coil will stop removing moisture from the air when the humidity has reached 60%. A higher coil temperature will give you higher humidity. A lower coil temperature will give you lower humidity. The desired coil temperature can be maintained by using an EPR valve.

Again assuming 42F coil temperature, with 59F cooler temperature, the humidity could go as low as 55%. With a 54F cooler, the lower limit would be 65% RH. Of course, the upper limit would be the 95% RH provided by opening the door.

Quote:

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Originally posted by Rory
If you refrigeration experts (were going to do this) how would you go about doing it?

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Hi Rory,

Well, I do it all the time. ;)


What I DO, is load calc the load of the space (say 55degF room with 80degF entering - indoor air), and select a condensing unit at a bout a 20 hour run time for the load (at 110F ambient - Texas ya'know ;) ) at a 35degF evaporating temperature. Then I select a fan coil whose rated capacity would give me a 16 to 20degF TD. Whereas for a 55F room, I would have a 35F evaporating temperature.

.. then I would install it. I have custom spec'd and installed refrigeration for the wine cellars of the Texas Rangers (baseball team) coach's house (amongst others). :D .... No complaints!

Mind you, that if the RH is too high... you start growing mold (on your corks) and the labels on the bottles get wet. You may have a $1,000,000.00 bottle of wine but when the $.75 label falls off, it's worth nothing! :eek:

if you are familiar with the wine refrigeration manufacturer sites, you've probably seen the cheat sheets on unit selection. Those are pretty accurate for load calc purposes that I have seen.

Cheers :)

OH! and a PS - put your vapor barrier on the outside walls of your wine room. The vapor pressure will be higher in the occupied space, and you want to insulate the vapor barrier, so it won;t get cold and cause condensation in your walls, floors or ceiling. ;)

Sounds good, herefishy. 35F refrigerant temperature would give you a somewhat higher coil temperature, and therefore leaving air temperature, which puts in right in the ballpark. :)

Do you use an EPR for positive limit, or is the RH not that critical?

Quote:

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Originally posted by Rory
I think that I can maintain outside humidity at 55% - 75%. If I open the cabinet fairly regularly, which I plan to do, and perhaps put a small pan of water in the bottom of the cabinet, I would have thought that it would be possible to keep humidity over 55%, which should be fine for the corks.

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Well, you're missing one point here.... and that is, you may have 55% to 75% RH in your occupied space at 75degF, but when the air enters (door is opened) and is cooled to 55F, the RH incresases (as Gary says to 95%), and that moisture needs to be removed. The colder the air, the fewer "grains" of moisture per lb. of air that can be suspended.

As such - high usage would increase the latent load (moisuture removal) requirements of the system.

Quote:

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Originally posted by Gary
Do you use an EPR for positive limit, or is the RH not that critical?

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Hi Gary.... I don't use an EPR. Mainly you just want to spec the system for a good run time (at proper TD) ;) The unit has to be running to remove the moisture. If you oversize the system... well, I'm preaching to the choir ;) you know what I mean. LOL!

Actually the RH IS very critical. But proper system balance, as I have described, ensures this.

I have yet to grow mold nor dry any corks, yet. :D

I haven't thought about it that much, but in the summer (when the A/C is on indoors), and the outdoor ambient is highest, the CU capcity is lowest and increases your run time for dehumidification. In the winter, the CU has high capacity and short(er) run times, but the indoor heating system is on which inherently lowers the vapor pressure of the infiltrating air, so the wine system load becomes mostly sensible.

Does that make sense to you?




Cheers

All except the part about winters. You have winters?

Quote:

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Originally posted by frank
As Herefishy says, you would be better off going for the purpose made cabinet.

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Rory,

You can still build your cabinet, just purchase one of those "window unit" type wine systems to install in your lovely and well-crafted storage cabinet! :p

Just select a proper unit for your cabinet. You can purchase them online - brands like breezair..... and others.

Quote:

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Originally posted by Gary
All except the part about winters. You have winters?

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ROFLMAO!!!!!!

Not to your standards....... But we wooses here in Texas DO turn the heat on when it hits a frigid 50degF! brrrrrrrrrrrr!

(But the vapor pressure is higher LOL!)

That's just like in Phoenix, Arizona, the say, "..But it's a dry heat". I lived there, and 120F in the Sonoran desert only feels like 105F in Texas.

.... All the energy n the universe is constant (and I consider it to be evenly distributed amongst the latent and sensible heat across the planet - not that I am well traveled, mind you :p)

If Rory is just building a reach-in type wine cabinet... he just needs to get a "window shaker" type refrigeration unit.... hell, they're cheap.

At 50F outdoor temp, you would need near 100% humidity to put any latent load at all on that cooler. The outdoor dewpoint drops like a rock.

Quote:

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Originally posted by Gary
At 50F outdoor temp, you would need near 100% humidity to put any latent load at all on that cooler. The outdoor dewpoint drops like a rock.

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I anticipate that his wine cabinet would be indoors. So the infiltrating 50degF (brrrrrr! LOL) air will be heated by the indoor enviromental system (further decreasing the inddor infiltrating RH).... aside from the moisture given off by the roasting of the chestnuts.

Well... the heating system doesn't add or remove moisture, it just changes the temperature, which changes the RH. When that air enters the cooler, its temperature drops, raising the RH back up. But the cooler is warmer than the outdoor air, so the RH is less than it was when that air was outdoors.

Wondering if that makes sense. I know what I mean... LOL

... water vapour .... has a vapour-pressure/dewpoint relationship from which the Relative humidity is derived?

Relative Humidity Versus Dew Point
What's The Difference?
During the summer, the buzz word is often "humidity." Driving to work in the morning, one can often hear one of the morning shows going on about how high the humidity is so early in the morning.

But, in reality it is the dew point temperature that makes being outside as uncomfortable as it can be during the summer, and not necessarily the relative humidity. Let's explore the differences.

Relative Humidity
The true definition of relative humidity (RH), is the ratio of the amount of water vapor actually in the air compared to the maximum amount of water vapor the air can hold at that particular temperature (and pressure). It is the ratio of the air's water vapor content to its capacity:

amount of water
vapor in the air
RH = -----------------------
amount of water vapor
the air can hold

Relative humidity is given as a percent. So, air with a 50 percent relative humidity actually contains one-half the amount of water vapor it could hold. Air with 100 percent relative humidity is said to be saturated because it is filled to capacity with vapor. If we increase or decrease the amount of water vapor in the air, the relative humidity will change.

In many places, the air's total vapor content varies only slightly during an entire day, and so it is the changing air temperature that primarily regulates the full variation in relative humidity. As the air cools during the night, the relative humidity increases. Normally, the highest relative humidity occurs in the morning, during the coolest part of the day. As the air warms during the day, the relative humidity drecreases, with the lowest values usually occurring dring the warmest part of the afternoon. However, the relative humidity combined warm temperatures create the humiture or heat index which feels warmer than the actual temperature.

Dew Point Temperature
The dew point temperature is defined as being the temperature the air must be cooled (at constant pressure and constant water vapor content) for saturation to occur. When the dew point is below freezing, it is commonly referred to as the frost point.

The dew point is an important measurement used to predict the formation of dew, frost, fog, and even the minimum temperature. Since atmospheric pressure varies only slightly at the earth's surface, the dew point is a good indicator of the air's water vapor content. High dew points indicate high water vapor content; low dew points indicate low.

The difference between air temperature and dew point can indicate whether the relative humidity is low or high. When the air temperature and dew point are far apart, the relative humidity is low; when they are close to the same value, the relative humidity is high. When the air temperature and dew point are equal, the relative humidity is 100%.

So, next time you step outside you'll know if the relative humidity high, or if the dew point is high.

I'm kinda partial to bumper sticker explanations, myself. :D

Different strokes for different folks. :D

Water vapour pressure

In a closed container partly filled with water there will be some water vapour in the space above the water. The concentration of water vapour depends only on the temperature. It is not dependent on the amount of water and is only very slightly influenced by the presence of air in the container.

The water vapour exerts a pressure on the walls of the container. The empirical equations given below give a good approximation to the saturation water vapour pressure at temperatures within the limits of the earth's climate.

Saturation vapour pressure, ps, in pascals:
ps = 610.78 *exp( t / ( t + 238.3 ) *17.2694 )
where t is the temperature in degrees Celsius

The svp below freezing can be corrected after using the equation above, thus:
ps ice = -4.86 + 0.855*ps + 0.000244*ps2

The next formula gives a direct result for the saturation vapour pressure over ice:
ps ice = exp( -6140.4 / ( 273 + t ) + 28.916 )

The pascal is the SI unit of pressure = newtons / m2. Atmospheric pressure is about 100,000 Pa (standard atmospheric pressure is defined as 101,300 Pa).



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Water vapour concentration

The relationship between vapour pressure and concentration is defined for any gas by the equation:
p = nRT/V
p is the pressure in Pa, V is the volume in cubic metres, T is the temperature in degrees Kelvin (degrees Celsius + 273.16), n is the quantity of gas expressed in molar mass ( 0.018 kg in the case of water ), R is the gas constant: 8.31 Joules/mol/m3

To convert the water vapour pressure to concentration in kg/m3: ( Kg / 0.018 ) / V = p / RT

kg/m3 = 0.002166 *p / ( t + 273.16 ) where p is the actual vapour pressure



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Relative Humidity

The Relative Humidity (RH) is the ratio of the actual water vapour pressure to the saturation water vapour pressure at the prevailing temperature.

RH = p/ps

RH is usually expressed as a percentage rather than as a fraction.

The RH is a ratio. It does not define the water content of the air unless the temperature is given. The reason RH is so much used in conservation is that most organic materials have an equilibrium water content that is mainly determined by the RH and is only slightly influenced by temperature.

Notice that air is not involved in the definition of RH. Airless space can have a RH. Air is the transporter of water vapour in the atmosphere and in air conditioning systems, so the phrase "RH of the air" is commonly used, and only occasionally misleading. The independence of RH from atmospheric pressure is not important on the ground, but it does have some relevance to calculations concerning air transport of works of art and conservation by freeze drying and the twilight zone.


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The Dew Point

The water vapour content of air is often quoted as dew point. This is the temperature to which the air must be cooled before dew condenses from it. At this temperature the actual water vapour content of the air is equal to the saturation water vapour pressure. The dew point is usually calculated from the RH. First one calculates ps, the saturation vapour pressure at the ambient temperature. The actual water vapour pressure, pa, is:

pa= ps * RH% / 100

The next step is to calculate the temperature at which pa would be the saturation vapour pressure. This means running backwards the equation given above for deriving saturation vapour pressure from temperature:

Let w = ln ( pa/ 610.78 )
Dew point = w *238.3 / ( 17.294 - w )

This calculation is often used to judge the probability of condensation on windows and within walls and roofs of humidified buildings.

The dew point can also be measured directly by cooling a mirror until it fogs. The RH is then given by the ratio

RH = 100 * ps dewpoint/psambient



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Concentration of water vapour in air

It is sometimes convenient to quote water vapour concentration as kg/kg of dry air. This is used in air conditioning calculations and is quoted on psychrometric charts. The following calculations for water vapour concentration in air apply at ground level.

Dry air has a molar mass of 0.029 kg. It is denser than water vapour, which has a molar mass of 0.018 kg. Therefore, humid air is lighter than dry air. If the total atmospheric pressure is P and the water vapour pressure is p, the partial pressure of the dry air component is P - p . The weight ratio of the two components, water vapour and dry air is:

kg water vapour / kg dry air = 0.018 *p / ( 0.029 *(P - p ) )
= 0.62 *p / (P - p )

At room temperature P - p is nearly equal to P, which at ground level is close to 100,000 Pa, so, approximately:

kg water vapour / kg dry air = 0.62 *10-5 *p



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Thermal properties of damp air

The heat content, usually called the enthalpy, of air rises with increasing water content. This hidden heat, called latent heat by air conditioning engineers, has to be supplied or removed in order to change the relative humidity of air, even at a constant temperature. This is relevant to conservators. The transfer of heat from an air stream to a wet surface, which releases water vapour to the air stream at the same time as it cools it, is the basis for psychrometry and many other microclimatic phenomena. Control of heat transfer can be used to control the drying and wetting of materials during conservation treatment.

The enthalpy of dry air is not known. Air at zero degrees celsius is defined to have zero enthalpy. The enthalpy, in kJ/kg, at any temperature, t, between 0 and 60C is approximately:

h = 1.007t - 0.026 below zero: h = 1.005t

The enthalpy of liquid water is also defined to be zero at zero degrees celsius. To turn liquid water to vapour at the same temperature requires a very considerable amount of heat energy: 2501 kJ/kg at 0C

At temperature t the heat content of water vapour is:

hw = 2501 + 1.84t

Notice that water vapour, once generated, also requires more heat than dry air to raise its temperature further: 1.84 kJ/kg.C against about 1 kJ/kg.C for dry air.

The enthalpy of moist air, in kJ/kg, is therefore:

h = (1.007*t - 0.026) + g*(2501 + 1.84*t)
g is the water content in kg/kg of dry air



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The Psychrometer

The final formula in this collection is the psychrometric equation. The psychrometer is the nearest to an absolute method of measuring RH that the conservator ever needs. It is more reliable than electronic devices, because it depends on the calibration of thermometers or temperature sensors, which are much more reliable than electrical RH sensors. The only limitation to the psychrometer is that it is difficult to use in confined spaces (not because it needs to be whirled around but because it releases water vapour).

The psychrometer, or wet and dry bulb thermometer, responds to the RH of the air in this way:

Unsaturated air evaporates water from the wet wick. The heat required to evaporate the water into the air stream is taken from the air stream, which cools in contact with the wet surface, thus cooling the thermometer beneath it. An equilibrium wet surface temperature is reached which is very roughly half way between ambient temperature and dew point temperature.

The air's potential to absorb water is proportional to the difference between the mole fraction, ma, of water vapour in the ambient air and the mole fraction, mw, of water vapour in the saturated air at the wet surface. It is this capacity to carry away water vapour which drives the temperature down to tw, the wet thermometer temperature, from the ambient temperature ta :
( mw - ma) = B( ta- tw)
B is a constant, whose numerical value can be derived theoretically by some rather complicated physics (see the reference below).

The water vapour concentration is expressed here as mole fraction in air, rather than as vapour pressure. Air is involved in the psychrometric equation, because it brings the heat required to evaporate water from the wet surface. The constant B is therefore dependent on total air pressure, P. However the mole fraction, m, is simply the ratio of vapour pressure p to total pressure P: p/P. The air pressure is the same for both ambient air and air in contact with the wet surface, so the constant B can be modified to a new value, A, which incorporates the pressure, allowing the molar fractions to be replaced by the corresponding vapour pressures:

pw - pa= A* ( ta- tw)

The relative humidity (as already defined) is the ratio of pa, the actual water vapour pressure of the air, to ps, the saturation water vapour pressure at ambient temperature.

RH% = 100 *pa/ ps = 100 *( pw - ( ta- tw) * 63) / ps
When the wet thermometer is frozen the constant changes to 56

The fact that there are a bunch of people having fun with the question, and are also having fun with speaking directly to one-another's expertise (which by definition means "slightly" over my head) is very neat.

I need to try to absorb these posts tomorrow morning. Let me add a couple of clarifications. The cabinet will indeed be indoors. Unlike Texas, we do have winters in Canada (although I seem recall some pretty chilly weather in January in the great State of the former Governor, and great character, Ann Richards). I keep my house at about 68-70 degrees F, but the natural humidity level and temperature need to be varied during the winter (cold, low humidity) and summer (sometimes damn hot, high humidity). It's a lot like upper New York State.

Which leaves the question of the temperature and humidity of the cabinet in this manipulated environment.

Is the question of humidity really that complicated? Before I bought a dehumidifier for my apartment, I kept my upright piano happy by putting a container of water in the bottom of the frame during the winter. Worked fine.

Anyway, I asked a question, if anyone wants to humour me, about HOW you would do this if you chose to do so.

P.S. to the Brits: Of course, if I were in my favourite place in the UK (Cowes, on the Isle of Wight), I could probably create a space that would have great temperature and humidity year round without refrigeration. But I'm not. I'm in Ottawa, Canada, where one tends to manipulate one's evirnonment a tad.

Rory, re-read the entire thread. I think you re-checked the thread after several pages of posts. You last left two pages ago. LOL!

herefishy,

Like I said, I have to carefully read through these posts, including your two-part dissertation on the weather and dew points. I figured that it would be a good idea to post this in the "practical application section" of this forum, but I'm starting to realize that it should have been in the "fundamentals section" :)

By the way, in searching the archives to find something on this subject, I did come across a thread in which you expressed strong views on selecting the right cooling system for the application. Very helpful it was, too.

Keeping in mind that the room temperature and humidity sets the upper limits for the humidity in the cooler, at 70F, do not allow the RH to drop below 35% (which can easily happen in a 'real' winter), or this can negatively affect the humidity in the cooler. For your own health and comfort, as well as the furnishings in your home, you want to keep it around 50% year round, anyway. :D

Quote:

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Ideally, the home's dew point would never drop to below about 4.7°C

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Which at 70F, would be 35% RH. :D

Quote:

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Originally posted by Marc O'Brien
I'm hoping you have read this material, fishy, it would make for a decent start along the journey of understanding psychrometrics :)

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:D Oh yes indeed, Marc. And I really appreciate you prompting me to investigate it. I learned a lot, and that is what we are here for.

Thanks ;)

What would be the effect of making the long term storage container (fridge) air tight and then drawing a vacuum within around the bottles of wine?

Aside from popping the corks?

Thanks all for the comments and suggestions. They have been very helpful.

No one mentioned using a psychrometric chart. I assume you are all familiar with it and don't resort to mirrors and equations????

ASHRAE has a psychrometric analysis CD available at www.ashrae.org

These long threads are hard to read. It's not easy to jump into something with 50 different conversations going on.

I believe there was good discussion regarding dew points and relative humidity, etc. Much of this disucssion was looking at a psychrometric chart and using words, mirrors, and equations. The lesser part of this discussion was answering the original question posed by Rory. But he received a practical answer or two.

Rory receives my vote for inspiring the most activity and debate within a short period of time during the month of September in the year 2003 within the forums of refrigeration-engineer.com.

Maybe a Tee-shirt could be in order when he commissions his unit and provides us with a report out?

Rest assured that all of my observations were made with psych chart in hand, Rog. :D

Quote:

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Originally posted by Marc O'Brien
I was using aspects of my online calculator, I hope it is sufficiently accurate for practical purposes.

http://fridgetech.com/calculators/ahucalc.html

I'm glad RogGoetsch has also heard of the chart.

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Sorry, Marc, no slight intended. It's just that it's one of the most useful tools I have used (next to the p-h diagram) and I was surprised not to read a single reference to it here.

For anyone for whom this subject is of further interest, the Trane company produced a big laminated psychrometric chart (11"x17") in the 70's that has wonderfully complete instructions, definitions, symbols, properties, etc. printed on the back. It is still available in both English & metric units from www.trane.com/bookstore/

I had another for low temp work by Carrier, I think. (Now on permanent loan to a friend in that end of the business) and every year I salivate at the idea of getting the Ashrae CD, but in my present work it would just be a luxury.

If something has practical hands-on value to me as a service tech, then I am interested. I have found a few aspects of the psych chart which serve a useful purpose from my perspective. Beyond that, I have no interest in learning the ins and outs of a psych chart, so it needn't be "COMPLETE".

I made a wine cooler for my boss one time. All I did was replace the LT comp with HT compressor and change the valve to match. I also mounted the CU on 1" of soft rubber. I let the condensate drain into the box with an overflow at about 1". It served as a vacuum break as well.

If you wanted to display the wine, you could use a floral box. They tend to be cheaper than wine boxes.

Quote:

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Originally Posted by superheat

If you wanted to display the wine, you could use a floral box. They tend to be cheaper than wine boxes.

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Hi,

The floral box is designed at about a 7degF T.D. in order to maintain high humidity levels (>90% R.H.). Wine should be kept at an R.H. of about 55% to 65%, primarily to keep mold from forming on the corks, and not damage the labels (moisture / condensation).

Accordingly, Wine room systems are designed at a 12degF to 15degF T.D., and preferably at long runtimes of 18 to 20 hours/day (for de-humidification).

In the case of short-term storage (merchandiser) however, I guess the conditions would not be that much of a concern.

... That is my experience.... (FWIW)

Cheers!