The list of abbreviations used in a set of engineering drawings varies from office to office.  Be sure to check the front section of the drawing set for the abbreviations used within. AAir or Compressed Air CFMCubic Feet per Minute CTBDCooling Tower Blow Down EAEach or Exhaust Air EAHUExhaust Air Handling Unit FAFree Area or Fire Alarm FDFloor Drain, Fire Damper, or Fire Department HPHorsepower or High Point HZHertz (Cycles per Second) NCNoise Criteria or Normally Closed PCFPounds per Cubic Foot PSIPounds per Square Inch PSIAPounds per Square Inch - Absolute PSIDPounds per Square Inch - Differential PSIGPounds per Square Inch - Gauge SDSmoke Detector or Smoke Damper SFDCombination Smoke / Fire Damper TEFCTotally Enclosed Fan Cooled TON12,000 BTUH (Cooling Capacity) We are here to help you stay smart on today’s heating and cooling solutions. There are many types of specialized HVAC technology used in commercial buildings and these are often much different from those terms used in common residential applications.

We thought it would be helpful to provide a summary list of the various types of commercial air conditioning systems used in the US today. Reviewing this list prior to or during conversations with your HVAC contractor might allow you to be more informed and less confused about the solutions being proposed for your commercial air conditioning needs.why put ac unit on the roof Variable Air Volume (VAV) – Single duct air system with varying airflow. mount a window air conditionerSupply air temperature can be controlled based on heating/cooling demand or reset based on outside air temperature. calculator for ac unitsVAV systems may include a terminal reheat box for better humidity and temperature control. Terminal fan powered boxes may be used for better zone control.

Constant Air Volume (CAV) – Single duct air system with constant airflow. Supply air temperature varies based on a call for heat or cooling from the thermostat. Variable Refrigerant Flow (VRF) – A heat-pump system that uses refrigerant as the heating and cooling medium. One condensing unit can serve multiple evaporators to condition the space. The heat recovery option allows the evaporators connected to the same condensing unit be in heating and cooling mode at the same time. This reduces the energy consumption required to heat and cool the spaces because less energy is wasted to the outdoors or condenser water loop. Chilled beams (active and passive) – A chilled beam is the terminal unit that conditions the space. The chilled beam includes a heating and cooling coil. Active chilled beams have air (typically ventilation air) introduced into the chilled beam to increase the capacity by increasing the induction of the unit. Passive chilled beams don’t have air introduced into the unit and heats and cools based on induction only.

Chilled beam systems save fan energy because of the reduced airflow required. Humidity and cooling water temperature must be controlled to avoid condensation. Heat Pump (water to water, water to air, air to air) – Heat pumps can heat a source of heat or cooling. Heat pumps move energy from one location to another and the refrigeration process reverses between heating and cooling modes. Air source heat pumps use the outside air as its heat source in the heating mode and its heat sink in the cooling mode. Fan Coils (FCU) and Blower Coils (BCU) – A terminal unit which is capable of providing heating and/or cooling to a zone or a space. Ventilation air is typically provided by a dedicated outside air system which supplies outside air directly to the room or to the return ductwork in a ducted system. A fan coil unit contains an internal fan, heating coil and/or a cooling coil. Fan coil units can be noisy because the fan is within the space or close to the space. Unit Ventilators (UV) – Unit ventilators are typically exposed to the space where it is providing ventilation air and/or conditioning.

Unit ventilators consist of an internal fan, and a heating and/or cooling coil. Ventilation air is typically provided by the unit ventilator and can be mixed with return air prior to conditioning the supply air. Ceiling Fans – Ceiling fans can used as a stand-alone device to improve comfort and with an HVAC system to improve the comfort in a space. Displacement Ventilation – An air distribution system that provides cool air into a space at a low level and at a low velocity. The supply air is introduced near the floor level and rises into the thermal plumes that are formed by heat sources. The benefits of this system energy efficiency and improved comfort. The system saves energy because ventilation air can be reduced per ASHRAE 62.1 because of the low supply height and high return height. The system improves comfort because it removes contaminants associated with heat sources. Geothermal – Geothermal systems use the earths internal energy to transfer heat. Heat transfer for a geothermal system is typically completed through a ground loop, pond/lake loop or a well loop.

Hybrid geothermal – A hybrid geothermal system consists of a typical geothermal well field and a heating/cooling element to offset the peak thermal load difference between the heating and cooling season. In cooling mode, typically a fluid cooler, cooling tower or heat pump is used to provide additional cooling for the system. In the heating mode, typically a boiler or heat pump is used to provide additional heating for the system. A hybrid geothermal system can lower the initial cost of the system by reducing the well field size with a minimal reduction in energy efficiency. The cost reduction and energy efficiency difference varies depending on the location, building load and amount of extra capacity that is required.I'm sure you'll understand that I can't give a definitive answer without seeing the full designs, but I can certainly... provide some issues and concerns I would want addressed if I were consulting on such a project. You don't define what you consider "high density", but I'm going to regard it as more than 5,000 watts per cabinet.

(Some people will say that 4,000, or even 3,500 Watts, is the "break point", but those arguments are immaterial to the points I want to make.) Neither do you indicate if your CRAC units are for under-floor or overhead cooling. If under-floor, be aware that you can't properly cool a true "high density" data center using only conventional computer room air conditioner (CRAC) units – and that assumes a raised floor of 24-inches or more in height, which is unlikely in most existing rooms. If overhead cooling is to be used, then it will be necessary to use a significant amount of duct work to properly channel both the supply and return air from and back to the CRAC Units. Simply filling the room with cold air won't do it. And my first suspicion in reading your question is that filing the room with cold air is exactly what the HVAC rep has in mind by doing this. Its just not that easy. Air flow, as you properly observe, is a critical part of making high density cooling work. There are other basic concerns about using Building Air.

First, data centers are normally expected to be "closed systems". The CRAC units operate by sensing return air, and if there is other air mixing with it, then the CRAC's will be getting the wrong message. Assume for the moment that some of the cool building air mixes with the warm return air heading back to the CRAC's, cooling it down. The CRAC's will think temperatures are great, and that less cooling is necessary, and will discharge air at an elevated temperature. (We have observed situations where simply locating an outside ventilation air duct over a CRAC unit have caused erratic air conditioner performance.) Data hardware discharge air, which is probably hotter than normal office return air, will also return to the building HVAC, causing it to put out more cold air, exacerbating the problem. In short, trying to combine two disparate systems, each of which is separately controlled, but each of which may be offsetting the other, creates complications that can be extremely difficult to design around, and virtually impossible to analyze and control after the fact.

It may be possible to achieve, but I wouldn't want the responsibility of trying. Another concern is humidity control (which is why a data center should have a vapor barrier – another possible problem in an existing room"). Data centers typically operate at a constant 40% - 50% relative humidity. They also typically operate at lower discharge air temperatures than building HVAC, with a very high "sensible to latent heat ratio". (Latent heat in offices results primarily from people and perspiration, which is minimal in a Data Center. Equipment gives off 100% Sensible Heat. Any air conditioning system handles both, but the designs are different depending on the relative amounts of each.) Here again, the two systems, each intended for completely different types of operations, and will likely oppose one another. Then there's the matter of air filtration. Data center air is heavily filtered through the CRAC units to minimize dirt accumulation in small electronic equipment fans and circuitry.

Filters are changed regularly (or at least should be) to ensure a cleaner than normal environment. Foot wipe pads are usually located at data center entrances to minimize the amount of dirt on people's shoes. Building air is never so well cleaned. (Just look at the ceilings around building air grills that have been in operation for a year or more, and see the amount of dirt accumulation.) Supplemental filters could be added before the air reaches the data center, but unless the HVAC system is designed specifically for this, and the filters regularly changed, they will probably restrict the amount of air to the point where the supplemental supply may be minimal anyway. In other words, if you depended on the cooling, and it isn't there because of the filters, you're in trouble at the outset. There's also the matter of fire protection. Fire, and fire suppression, inside a data center must be completely contained. Therefore, all ducts entering and leaving the data center must be provided with automatic fire dampers.

This is just another expense involved in trying to run building HVAC into the data center. Bringing in enough air to be worthwhile will require large ducts and, of course, large fire dampers. And lastly, there's the ever-present question of "availability". The data center runs 24 hours, seven days a week. It may even have generator backup. Is the building air necessary to maintaining operations? If so, is it equally reliable? If it is, and it's not, then why is it being used? There are a number of very special techniques for handling high density design. I would not generally consider adding building HVAC to be one of them. The first requirement is to build an excellent "cooling foundation" with conventional CRAC units, properly sized and located relative to the equipment. The various special means of supplementing the cooling can then be added, as needed and as appropriate, depending on the actual loads, their locations, and a variety of other conditions. Building HVAC cannot provide that flexibility, even if could provide a worthwhile addition to cooling capacity, which I very much doubt it can.