Part 1: Evolution of VAV Systems, and Dedicated Outdoor Air Systems as Alternative HVAC Strategy Understanding Displacement Ventilation, Underfloor Air Distribution as Alternative HVAC Strategies Understanding Radiant Heating/Cooling and Demand-Control Ventilation as Alternative HVAC Strategies Part 1 of a 3-part article describing the pros and cons of five alternative HVAC approaches HVAC   Article Use Policy In today’s commercial buildings, all-air variable air volume (VAV) systems conserve energy, control humidity, and can be installed at a reasonable first cost to meet a facility’s HVAC needs. But a number of alternative HVAC strategies — dedicated outdoor air systems, displacement ventilation, underfloor air distribution, and radiant heating/cooling — are thought to offer greater efficiencies and better performance. Before we delve into these alternative choices, though, it’s important to first understand the baseline and how the industry historically evolved to the point of using the standard VAV systems.

When air conditioning units where first introduced in the 1930s, large, constant-air-volume systems were used to cool down large volumes of air and extract moisture from any given space. Eventually, multi-zone systems gave users control over the temperature in different spaces. However, air volume remained constant. Through the process of cooling down and warming up large volumes of air in multiple zones, humidity stayed low, but these systems required lots of energy to operate. During the 1970s energy crisis, VAV systems came onto the scene. By modulating air volume and only using as much cool air as required to ventilate a space or meet a cooling load, VAV systems significantly reduced the energy and operational expenditure of buildings. When selecting an HVAC system, the most important characteristics are: • Comfort and zone control Because they meet the majority of these requirements, sturdy and dependable VAV systems have remained the standard for the past few decades.

Managing the humidity load, leveraging zone control, maintaining comfort, and enabling engineers to scale up or down a project by adding as many VAV boxes as required, VAV systems enable facility managers to determine how much outside air to bring into a building. The upshot is that VAV systems get the job done and the systems can be built out at reasonable cost. So why fix what isn’t broken? The answer is that HVAC systems can be performing at a higher level. In the United States, humidity control is a big priority. As stated, VAV does the trick; however, humidity management is not one of VAV’s greatest strengths. In fact, humidity control can be compromised when air volume is varied, which raises the question: Would other technologies be able to offer more comfort, control, and reliability while maintaining energy efficiency? There are five options to consider, and in the remainder of this article we’ll take a look at each, starting with: The main principle of these systems is splitting humidity control and ventilation from heating and cooling.

With dedicated outside air systems (DOAS), the advantages of constant air volume — namely, reliability and humidity control — can be more economically leveraged by specifying it only for the ventilation and dehumidification aspects of the system. The DOAS can then be coupled with a number of other systems — i.e., chilled beams, induction units, fan coils, etc. — to facilitate heating and cooling. how to put freon in an ac window unitWith a high level of humidity control, the space doesn’t have to be cooled quite as much, because people are generally comfortable at higher temperatures if the humidity is controlled.cost of hvac diffusers DOAS has been popular in Europe for some time, where it is often used to control mild humidity and deliver outside air, while fan coil units or radiant cooling/heating modulate indoor air temperature.car air conditioning repairs hoppers crossing

But where humidity is a concern, DOAS is an even more compelling choice. It’s important to understand, though, that coupling DOAS with a heating/cooling system — particularly a fluid-based technology requiring pipes and valves — will come at a higher first cost. In typical commercial spaces, the perceived benefit of installing two systems may not convince building owners that the higher first cost is worth it. However, in specialized spaces, such as museums, schools, or high-end office buildings where owners are trying to attract a high-profile tenant, DOAS can be a good fit. Part 1: Evolution of VAV Systems, and Dedicated Outdoor Air Systems as Alternative HVAC Strategy Part 2: Understanding Displacement Ventilation, Underfloor Air Distribution as Alternative HVAC Strategies Part 3: Understanding Radiant Heating/Cooling and Demand-Control Ventilation as Alternative HVAC Strategies For more info on Through the Wall, Window Units, Portable Air Conditioners or other LG Products...

Written COST or Floor Space concerns. The majority of HVAC units used for cooling today will utilize forced air so explanations of hot air rising etc are an incomplete picture of the decision.  First of all, are you sure the air conditioner (AC) is ceiling hung?  You may notice registers in the ceiling or even a box, but that does not mean the AC unit is in the ceiling.  You could have a VAV (variable air volume) system, or other system.  The AC could then be located in a chiller room or a mechanical room etc. So understanding what system is installed lets us figure what reasons influenced the decision.  Having an AC unit installed in a mechanical room where service is easy would be the most desirable place for continue maintenance costs.  The reason it is not on the ground in a closet is usually because of cost.  The cost of floor space can be very expensive in major cities.  Therefore the VAV systems that utilive chill water loops or federal style self contained unit systems that utilize condenser water loops exist. 

They centralize a smaller foot print, use ceiling mounter supply air ducts and typically a plenum return system.  By installing the low maintenance/ long life simple components in the drop ceiling but keeping the main AC system floor mounted you save on floor space while allowing ease of access for maintenance. Sometimes you install the ac system in the ceiling as well.  This can be done to serve an area without losing any floor space at all.    Written Its not advisable to have cooling on floor , as there are some challenges in having cooling through floor .. Cold air is denser than hot air and tends to settle at bottom which can increase the temp of the flooring, cold floors are not preferred for human comfort , if cooling is from height it won't cool the floor as it gains heat when and becomes lighter.Humans have temp sensors that provides surrounding temp information to brain , feet is one of the most sensitive receptors,and feet need a bit higher temp than the torso, that's why you feel good in winter when u wear socks also it's always difficult to walk on cold floors.

Floor  vents which means it's difficult to place a carpet or any other furniture on floor which can impact the effect of cooling in your room, also it effects your cooling impact you may not recieve the 24c temp it could be 25 or 26 depending on your heat generating units that are placed on the floor, laptops or lamps.Brain and spine are important parts of body that can assess the situation of the body, both have to be cooled 1st , if the cold air is coming through floor by the time it reaches the torso and above it would have gained certain heat and you can expect there could be an increase in temp.Colling at height allow air to pass but a floor cooling has restrictions due to the items places on the floor , in this case it puts a pressure on airflow that can be generated by fan/blowerHaving cooling on floors can be a expensive solution as you are paying floor space / carpet area etc ..Written According to the basic physics, Hot air is less denser and cold air is more denser. So what will happen when a higher weight object is dropped in a lower weight liquid.