What are ideal temperature and humidity parameters for wine storage?

An ideal temperature for wine storage is 55°F with a 60% relative humidity. This temperature and RH will allow the wines to mature slowly and keep the corks from drying out. Higher temperature and RH cause faster maturing of the wines and the potential for mold and spoiling of the labels. Whatever temperature is chosen, it should remain constant. Fluctuations in temperature stress the wine and cause the liquid in the bottle to expand and contract. This expansion and contraction puts pressure on the seal of the cork against the bottle and causes premature leakage and spoilage.

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What is the most important factor to consider when selecting a wine cellar cooling unit?

In all cases, quality should be a primary consideration. A cheap initial price will soon be forgotten when the unit fails and stresses your wine, not to mention your nerves in trying to get it serviced. Quality should be “built-in” at the factory using commercial/industrial grade components that meet safety and reliability standards. Exposed sheet metal components should be aluminum with a powder-coated finish to prevent corrosion in the cold and high humidity conditions of wine cellars and basements. The manufacturer should have a reputation for quality and reliability; not only in the product but also in the service it provides its customers. Buy only units that have met the ETL/UL/CSA safety standards and are so labeled.

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What other safety features should my wine cellar cooling unit offer?

Built-in safety features are important because they protect certain components in case of some malfunction. High and low refrigerant pressure switches are used to protect the compressor. Timers are used to prevent the unit from short-cycling. Minimum temperature differentials are used to prevent switching between heating and cooling too rapidly.

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What size and style of wine cellar cooling unit do I need? 

Cooling units are made in many different sizes and shapes. The most common is the through-wall style generally used in smaller cellars where the cooler is mounted into a wall opening and blows directly into the cellar. Another popular style is the remote, ducted unit. They are generally quieter and offer more flexibility in design and installation. They also come in larger capacities for larger cellars. The split system type coolers are used when ducting is not feasible or when the condenser must be installed outdoors. Unlike the first two styles that can be installed by the homeowner or contractor, the split system must be installed by licensed electrical and refrigeration technicians.

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How do I select the correct sized wine cellar cooling system?

The number of bottles or the cubic footage of the cellar is not sufficient to select the size or capacity of the cooling unit. These are only two of the variables that enter into the calculations for properly selecting a cooling unit. The most important is the amount of insulation and the temperatures of the surrounding spaces. But other variables such as frequency of door openings, turn-over of wines, lighting intensity and duration, number, size and insulation of doors and windows, etc., all enter into the calculations. Therefore it is best if the calculation is done by a professional or by using a professional load calculation program.

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How are wine cellar cooling units rated? 

Air conditioning units should be rated at close to the intended operating temperatures and humidity. For a room air conditioner, this means rating around 72°F and 50% RH. For a wine cellar, this means around 55°F and 60%RH. Unfortunately, many wine cellar cooling units are listed with capacities based on room conditions rather than cellar conditions. This overstates their operating capacities by a factor of 35% to 50%.

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What should I know about installing a wine cellar cooling unit? 

Ease of installation and flexibility are important because of the potential extra costs. Any system that is not completely assembled and tested in the factory will require more highly skilled and licensed contractors in the field. This can be very costly, time consuming and often with inferior results.

• Through-wall units are the least flexible in that they must be installed in a cellar wall area that is open to the cellar and doesn’t interfere with the racking but also must be adjacent to a space, which can tolerate the heat and noise from the condenser side of the unit.
  
  
• Split systems offer better flexibility because the evaporator fan located inside the cellar is connected to the condenser located outside with insulated refrigeration tubing that can be installed unobtrusively.
  
  
  
• Ducted systems offer the greatest flexibility because only the inlet and outlet grilles, which are flush mounted, are located in the cellar. The unit itself can be mounted most anywhere and is connected to the cellar with insulated ducts.
  
  

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What about noise? 

Through-wall units are the noisiest because all the mechanical equipment is located right in the cellar with openings facing directly out. Split systems also have the evaporator fan located directly in the cellar. The quietest systems are the ducted units because the unit is more contained, can be located away from the cellar and have insulated ducts to absorb the air noise generated by the fans. The quietest units are those that can have ducts on both the evaporator and condenser sides.

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Tell me more about supply air and return air grilles.

Supply and return air grilles should be located so that airflow is directed to maximize the exchange of air in the cellar. Since the air entering the cellar will be colder, it will tend to fall as it flows across the cellar. And since the warmer cellar air will tend to rise, it is recommended that both the supply and return air grilles be placed up high on the wall or in the ceiling. This will give the best exchange of air and keep the most constant temperature. There will always be a slight temperature differential between floor and ceiling, and between supply air and return air. This temperature difference can be used to an advantage to keep certain wines or champagnes slightly colder or warmer than others.

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What is the difference between using an external drain vs. a boil-off coil inside the unit?

All cooling units, especially during hot humid weather, will periodically cool the air below the dew point of the cellar thereby removing excess moisture and preventing too high a humidity. The moisture forms on the cold cooling coil surface and drips into a drain pan. It is then either piped to a drain outside the unit or into the condenser section of the unit where it comes in contact with hot gas tubing from the compressor and is boiled off. There are two problems with this. The first is the corrosion that occurs on the hot gas tubing, which will cause refrigerant leaks. The second is that this moisture is then just added back into the air-stream of the condenser exhaust where it can find its way easily back into the cellar. The most reliable and least costly way to get rid of the excess moisture is to pipe it to a drain where it cannot get back into the basement or cellar.

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What is the difference between in-bottle liquid temperature control and wall mounted air temperature control?

When the cooling unit is controlled (turned on and off) by a sensor located in the liquid of a bottle sitting on a shelf, the wine itself will be subjected to the full temperature swing of the instrument. In other words, if the sensor and controller are rated at +/- 2°F, the wine temperature will change by 4°F with each on/off cycle. This will stress the wine and cause pre-mature aging. However, by sensing the cellar air temperature, even a +/-2°F thermostat will cause only a fraction of a degree change in the wine temperature. This is because of the thermal mass inertia of the liquid essentially insulated inside the glass bottle. The air temperature changes much faster than the liquid temperature as it is lighter and more sensitive to load variations. A good thermostat with a range of +/- 1°F will keep the wine at basically a constant temperature.

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Why is humidification so important for the proper storage of wine?

Low humidity causes dryness of the corks resulting in loss of liquid in the bottles. High humidity causes mold and degradation of the labels and glue. Cooling units control both cooling and dehumidification. That is, they cool the cellar air down below its dew point, which causes moisture to condense out and drip into a drain pan. The water is then removed by an external drain line or re-evaporated by a heated coil in the external section of the unit. This combination of cooling and dehumidifying generally keeps the cellar at the proper temperature and humidity during the cooling season. A cooling unit alone cannot add moisture or humidify the cellar air. It needs a humidifier to do so. The best option is where the humidifier is integrated into the cooling unit so it operates and distributes the moisture evenly in the recirculating air. A free-standing humidifier can also be used but should be one controlled by a quality wall-mounted humidistat. Again, the humidifier should have a capacity rated at the temperature of a wine cellar and not at room temperature or even at furnace discharge temperature as many are.

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Should I heat my wine cellar?  

In many cases, especially in northern climates, the answer is yes. Any cellars that would be subject to ambient temperatures below 55°F should be protected with a heating coil. Without the ability to heat, a cooling unit can do nothing if the temperature in the cellar falls below the control setpoint. The best system is one where the heating is integrated into the cooling unit and works off the same thermostat. This prevents any overlap where a free-standing heater might be on at the same time the cooling unit is cooling. Again, with the cellar thermostat controlling both heating and cooling, the wine liquid temperature will remain constant throughout the year.

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What is a low ambient control option used for?

Low ambient control options are used when the condenser or outside portion of the unit will be exposed to cold outside air temperatures of 40°F or lower. For example, if the unit is located in a garage. The low ambient feature cycles the condenser fan on and off based on system pressures to maintain the right balance. The option also includes a compressor crankcase heater that keeps the oil within the system at elevated temperatures so it does not freeze.

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When should I spec a water-cooled option?

A water-cooled option might be of interest for any locations where water is plentiful like near a lake, well, or swimming pool. Instead of using ambient air to remove heat from the condenser, the water is used. This might be important where the heat cannot be ducted away conveniently or where the noise from a condenser fan would be objectionable. The heating of the water could also be a creative way to save energy.

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How do I frame out my wine cellar? 

Standard 2x4 studs can generally be used to frame the walls. However, 2x6 studs may be desirable for structural needs or if thicker insulation is used. Ceilings can be framed with furring strips against floor or roof joists, but care must be taken with the installation of the insulation and vapor barrier. The vapor barrier must be installed first and be looped up into the joist space to form a complete seal. The insulation is then pushed up into the joist space and held in place by the furring strips or other framing such as arches. If the walls are against an outside foundation wall, it is recommended that they not be installed directly against the foundation wall but with a minimum 1” gap to allow air to circulate and prevent condensation or mold from forming. It is easier if the vapor barrier is installed on the wall as it is framed on the floor before it is tipped up into place.

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What is the best way to insulate my wine cellar? 

The entire wine cellar should be insulated to conserve energy, stabilize temperatures and control humidity. Minimum fiberglass insulation should be 3 ½” in walls and 6” in ceiling, although 6” all around is better. If there is space below the floor, the floor should be insulated also. If the floor is concrete, no insulation is required. If the floor does not have a vapor barrier beneath it, a waterproof sealer is recommended before any other flooring such as wood or carpet is installed.

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Why is a vapor barrier important? 

A vapor barrier around the entire room is needed to control humidity. A minimum of 4 mil. plastic is recommended with seams overlapped and taped. The vapor barrier must be installed on the outside (or warm side) of the cellar insulation. This is to prevent condensation from forming on the vapor barrier, potentially wetting the insulation and forming mold.

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What about electrical outlets or lights?

Boxes for outlets, switches and fixtures should be sealed plastic boxes and any wiring penetrations should be caulked to prevent outside air from entering the cellar. Care must be taken with installing boxes and wiring to not degrade the vapor barrier or insulation. Any penetration of the vapor barrier should be sealed airtight.

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What kind of doors should I use?

Wine cellar doors should be fully insulated, similar to exterior doors. Any glass should be insulated thermo-pane to prevent sweating and fogging. The doors should have gaskets around the frame to seal against the door. Floor sweeps should be used to seal the opening between the floor and the bottom of the door. Hardware should be good quality, exterior grade to prevent sweating and possible rusting.

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What if I want to add windows to my cellar?

All windows should be of the insulated, double wall, thermo-pane type. The space between the window frame and wall studs should be packed with insulation and covered with the vapor barrier.

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Is it OK to put lights in my cellar? 

Lights add much to the atmosphere in a cellar but also add a heat load to the cooling unit. Therefore it is best to use low intensity lighting or ones where the transformers are located outside the cellar. Avoid recessed lights that penetrate into the insulation and vapor barrier.

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What type of wine rack works best?

Racks should be designed in consultation with one of the several experienced producers. Thought needs to be given to the layout and quantity of single, multiple or large format bottle configurations. Tables or wide shelves where cases or boxes can be set down to be opened is very useful. Do not block the supply or return air registers with shelving, racks or displays. The air needs to circulate freely.

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What if I need service and maintenance?

Service and maintenance is an important consideration since the equipment performance is dependent on being serviced and maintained properly. Filters on both the evaporator and condenser coils will protect them from dust and dirt building up inside the coils, reducing their capacity and efficiency. And it is very difficult to clean these types of coils. Access to the electrical and mechanical components is important is any service is needed. Many units, especially through-wall units, are not designed to be field serviced. They are often pop riveted closed and are not serviceable without completely removing the unit and sending it back to the factory.

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Who covers the warranty?

Manufacturers warrant their products according the terms and conditions in their literature to the original buyer. Since many wine cellar cooling units are purchased through dealers and catalogue houses, it is important to understand who will be providing the warranty and if you are covered by the manufacturer’s warranty. Optional extended warranties on such critical and costly items as the compressor (similar to the automotive power train extended warranties) should be considered especially on the larger capacity units.

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Wine Guardian® is a registered trademark of Air Innovations.