Wine Cellar 101

Whether you're new to the world of wine cellars or just need a quick reference for a concept, browse this alphabetical list of important terms related to cellars and cooling units.

Any bold words or phrases within definitions are also defined elsewhere in the glossary.

Air Handler - Systems designed to be located away from the cellar, with the cold air intake and cold air exhaust ducted to and from the cellar. This ducting allows the heat and noise from the cooling unit to be contained in a remote location. Air handlers can be configured as self-contained systems or as split systems.

BTUH – British Thermal Units per Hour, the unit of measure for expressing the thermal load, or the amount of energy required to heat or cool a space to a certain temperature in an hour. The amount of BTUH produced by a cooling unit depends on the surface area of the coils, the amount of airflow across those coils, and the temperature of those coils.

Cellar – The space where you keep your wine. Ideally, a wine cellar will have cool, constant temperatures in the range of 55° to 60°F, humidity levels around 60%, low light, and minimal vibrations or disturbances.

Cold Air Exhaust or Cold Air Discharge – Cold air emanating from a unit, which either blows directly into the cellar or is ducted into the cellar, and serves the function of cooling the space.

Cold Air Intake – Airflow from inside the cellar that enters the unit. In order to generate cold air exhaust, all cooling units must take in this air, which generally enters via the front of the unit.

Cold Side – The side of the cooling unit where the cold air intake and cold air exhaust are located. The evaporator coils are also located on the cold side of the cooling unit.

Compressor – The compressor is the main component in refrigeration system, and works by compressing the refrigerant gas into a high-pressure vapor and pushing the vapor through the condenser coils. As the vapor cools into a high-pressure liquid, the heat picked up by the refrigerant on the evaporator coils is rejected through the condenser coils. Then, the high-pressure liquid pushes through the expansion valve into the evaporator, where the liquid expands into gas, causing the evaporator temperature to drop.

Compressor Heater – A self-regulating electronic device attached to the compressor that adds heat to the compressor shell when the cellar temperature drops below 40°. Most cooling units do not come standard with compressor heaters. So, if the temperature of the fresh air intake or return ever falls below 40°F, you need to order a compressor heater modification to prevent damage to the compressor.

Coils – In the context of a refrigeration unit, "coils" can refer either to the condenser coils or to the evaporator coils. When using the term "coils," be sure to specify which kind of coils. If you are not sure which kind of coils, seek clarification from the manufacturer.

Condensation – As the cold air intake comes into contact with the evaporator coils, condensation will occur on the coils until the system reaches equilibrium, which is a function of the temperature of the coils, the rate of airflow, and the amount of moisture inside the cellar environment. The energy required to generate condensation is called the latent load.

Condenser – See condensing unit.

Condenser Coils – The compressor converts the refrigerant gas into a high-pressure vapor and pushes that vapor through the condenser coils, condensing it into a liquid. This process rejects the heat that is picked up by the refrigerant as it passes over the evaporator coils and disperses that heat through the condenser coils as the condenser fan pulls the fresh air intake across the coils.

Condenser Fan – A fan that pulls air from the ambient environment (fresh air intake) and blows it across condenser coils, creating the hot air exhaust.

Condensing Unit – Also referred to as a condenser, this key component of a refrigeration system primarily includes the compressor, the condenser coils, and the condenser fan(s). In self-contained systems, the condensing unit and the evaporator are attached and connected. In split systems, the condensing unit and the evaporator are separated.

Cooling Unit or Cooling System – Cooling units are designed to create and maintain specified temperature conditions in a given space. Most units serve only to lower the temperature of a given space, but some also provide heat when necessary. Some cooling units also have optional humidification modules that also will add moisture to a given space.

Wine cellar cooling units are supposed to maintain not only proper storage temperatures with minimal variations, but also ideal humidity conditions inside the cellar. Some brands do a better job than others at maintaining unvarying temperatures and ideal humidity under a variety of ambient conditions.

Drain Line – A way for condensation to exit the cooling unit. Condensation occurs on evaporator coils for the same reason that moisture collects on the outside surface of cold drinks in the summertime.

Ducted System – Systems designed to be ducted, usually on the cold side but sometimes on the hot side. Both self-contained systems and split systems can be ducted systems.

Ducting – Ducting allows air—cold or hot, intake or exhaust—to be transported from one location to another. Ducting can be made from foil (flex ducting), hard plastic, or sheet metal, and comes in many shapes and sizes. Ducting can be insulated or uninsulated, depending on the application. Each cooling system will have ducting size requirements based on the system’s airflow, which should be followed closely. When ducting cold air to and from a cellar, the ducting should be insulated to minimize the loss of BTUH as the cold air passes.

Evaporator – See evaporator coils.

Evaporator Coils – Coils in which the refrigerant liquid expands into gas, bringing down the temperature. As the evaporator fan pulls the cold air intake across the evaporator coils, it generates the cold air discharge.

Fan Cycling Switch – An electronic device wired to the condenser fan. If the temperature of the fresh air intake ever drops below 23°F, the fan cycling switch (in addition to the compressor heater) keeps the system operating properly and efficiently.

Fresh Air Intake or Fresh Air Return – A steady supply of cool air from outside of the cellar. In order to cool down the condenser coils and the compressor, all cooling units must have access to this airflow. Generally, the fresh air return comes from a temperature-controlled environment, otherwise a compressor heater and a fan cycling switch may be required. The fresh air return generally flows in at the back of the cooling unit.

Exterior Unit – An exterior unit is designed so that the condenser coils or the condensing unit can work outdoors and handle the external environment.

Hot Air Exhaust – The hot air generated by the cooling unit as the fresh air return passes over the condenser coils. This hot air exhaust must be managed carefully to ensure that it doesn't intermingle with the fresh air return. You should make sure that the space into which the hot air is exhausted is sufficiently large to ensure that the hot air dissipates rather than returning into the fresh air return.

Hot Side - The side of the cooling unit where the fresh air return, the hot air exhaust, and the condenser coils are located.

Humidity – The amount of moisture in the air, expressed as a percentage. Humidity is a relative figure, because the amount of moisture that can be held in the air increases as temperatures rise and decreases as temperatures fall. The ideal humidity for wine cellars is about 60%.

Indoor Unit – An indoor unit that cannot function outdoors or handle external conditions.

Infiltration – Air entering the cellar from an outside environment that is not climate-controlled. The amount of infiltration should be limited, because air from outside of the cellar will have more moisture than the air inside the cellar, and thus will create condensation on the evaporator coils and increase the latent load.

Insulation – Insulation is a material or substance used to keep warm spaces warm and cold spaces cold. The higher a material's R-value is, the better the insulation it provides.

Latent Load – The amount of energy, expressed in British Thermal Units per Hour (BTUH), required to condense the excess moisture that exists in the air inside a cellar.

Line Set – The copper tubing that connects the evaporator and the condensing unit in a split system. Typically, the line set includes 2 copper tubes, one insulated (the suction line), one uninsulated (the liquid line).

Moisture Barrier – See vapor barrier.

R-Value – The capacity of an insulating material to resist heat flow. The higher the R-value, the greater the insulating power. For example,

• The R-value of fiberglass batts typically ranges from 3.15 to 4.30 per inch, providing moderate resistance to heat at low thicknesses and higher resistance as thicknesses increase.
• The R-values of single-pane and double-pane glass (assuming .5" air space) are 0.91 and 2.04, respectively, which means that they offer much less insulating power than other insulating materials, such as fiberglass.
• The R-value of concrete is particularly low at 0.08 per inch and makes very poor insulation in contrast to common perceptions.

Wine cellars should be insulated with the highest possible R-value, either by using better materials or thicker insulation. This will result in more stable conditions inside the cellar, even as temperatures rise and fall outside the cellar, and will protect the cooling unit from running constantly to maintain the desired temperature inside the cellar.

Refrigerant – The working substance of a refrigerator. The refrigerant absorbs heat from inside the cellar as it passes through the evaporator coils and rejects heat outside the cellar as it passes through the condenser coils. At CellarPro, we use use R-134a refrigerant in all of our cooling units.

Self-Contained System – A system that is delivered fully charged and ready to use out of the box. Therefore, self-contained systems are the simplest kind to install, requiring only power and an opening in the wall where you can place the unit.

Split System – A system in which the evaporator is separate from the condensing unit, allowing the heat and noise from the condensing unit to be contained in a remote location. The evaporator and condensing unit must be connected by a copper line set, which allows the refrigerant to pass back and forth. In some configurations, wiring for electrical power also connects the evaporator and condensing unit. Only licensed HVAC/R technicians should install split systems, due to their complex set-ups.

Thermal Load – The amount of energy, expressed in British Thermal Units per Hour (BTUH), required to maintain your wine cellar at the desired cellar temperature. The variables required to calculate a thermal load include: the size of the cellar, the R-value of the insulation used in building the cellar, the desired cellar temperature, and the peak ambient temperature (or maximum temperature outside the cellar). Other factors, such as altitude, infiltration, ducting, areas of glass, and other heat sources, to name a few, may impact the final thermal load calculation and increase the required capacity of the cooling unit.

Vapor Barrier – A barrier designed to prevent moisture-laden air from infiltrating the cellar environment. You can create a vapor barrier by wrapping your cellar in plastic (typically 6 mil thick) or, alternatively, by adding closed-cell foam insulation while constructing the wine cellar. Without a vapor barrier, condensation will overburden the cooling unit, resulting in loss of efficiency due to the the latent load.

The long-term effects of excess moisture also include mold growth, drain line blockages, rust, and a shortened lifespan for your unit. A typical cooling unit warranty does not cover damage or problems caused by too much condensation, resulting from an ineffective vapor barrier.