The VFD will try to maintain the speed (RPM) of the fan so that the static pressure in the duct at the location of the static pressure sensor maintains some minimum set-point, such as 1.25” sp. The static pressure sensor sends a signal to the VFD and the speed of the fan is adjusted according to the set-point required. HRV is invented by Daikin Air Conditioning in 1992, it is now called the Total Heat Exchanger. This type of air conditioner recovers lost heat energy through ventilation equipment, reducing the load on the air conditioner while maintaining a comfortable and fresh environment. In addition, HRV can be used in conjunction with VRV systems, commercial split systems and other air conditioning systems, and can automatically switch ventilation modes to further improve energy-saving effects.

  1. Functionally, according to the requirements of the use environment, it can achieve constant temperature and humidity or simply provide fresh air.
  2. The Air Handler varies the amount of air flow (CFM) at the overall system level based on the demand required by the zone level VAV boxes, which vary air flow based on their local demand.
  3. OAC is a name called in Japan, which is used for air feeding into closed workshops, which is equivalent to fresh air treatment unit MAU or FAU.
  4. For a single VAV air handler that serves multiple thermal zones, the flow rate to each zone must be varied as well.
  5. These conditions/criteria could be the ‘real time’ demand for either heating or cooling, occupancy levels, window switches, time clocks or any number of other inputs from either the unit itself, the Building Management System or both.

The circulating air conditioning box is also called the indoor air circulation unit, which mainly sucks and discharges indoor air to ensure indoor air circulation. The outdoor unit is for air-cooled heat exchange, and the indoor units adopt the direct evaporative heat exchange. Fan coil units (FCU’s) are small single units that condition air and move it to the space via minimal ductwork. They can be used to manage small loads [KW], usually located in single rooms, recirculating the air. VAVs are like automated volume damper which is installed to regulate the flow of air in conditioned space according to the thermostat setting.

• VAV system generally have lower maintenance requirements as compared to the other systems. This is because there is no chilled water coil at the VAV terminal and, where non-fan powered VAV terminal are used, there is no filter at the unit. All the routine maintenance (filter replacement, condensate pan cleaning) is centrally located at the air handling unit, minimizing maintenance needed within the occupied spaces. As the pressure increases in the main supply duct because the VAV boxes are closing their dampers and are adjusting their dampers towards the minimum open setting, the air handler supply fan VFD slows down the fan. The opposite will happen due to the VAV boxes opening because of increased demand and the dampers are opening, in this case the VFD will cause the supply fan to speed up when the pressure in the main supply air duct drops. As the VAV boxes open or close due to demand called for by the temperature sensor in the space, the pressure in the main supply air duct will either increase or decrease.

This adjustment is typically performed during the commissioning stage of building construction and remains fixed for the lifespan of the unit. Some zones are in cooling mode with their dampers at different percentages of being open, while other zones are in heating and one zone is off and receiving minimum air for ventilation. This is a very basic diagram of how zones may differ and why it’s important to consider how spaces are grouped vav vs fcu together, as each space may have a different solar exposure and cooling load profile. As the sun travels across the sky the zone dampers will open or close depending on their need for heating or cooling. Alternatively, certain manufacturers employ custom-wound Permanent Split Capacitor (PSC) motors with speed taps in the windings. These taps are set to the desired speed levels for the specific design of the fan coil unit.

Unit ventilator

Using a DDC control system with VAV boxes that have a flow station and temperature sensor at the supply air discharge the system can determine the amount of reheat. The use of this strategy is required by Title-24 (California) and ASHRAE 90.1 for system that have DDC to the zone level. The static pressure setting in the main supply duct is reduced to a point where one VAV box damper is nearly full open. This would require that the VAV box actuators can report their damper position, best performed with an analog output. The pressure sensor in the duct will send a signal to the Variable Frequency Drive (VFD) causing the supply and return fans to slow down or reduce its RPM. If the pressure in the duct decreases because the VAV boxes are opening due to the need for additional cooling, the pressure sensor will send a signal to increase the fan speed (RPM).

The minimum CFM setpoint can be somewhere between 30% and 50% of the maximum cooling setpoint. Minimums are set by some code jurisdiction so that the minimum ventilation rate is always achieved. In California see Title-24 Sec 120.1 Requirements for Ventilation and Indoor Air Quality. This primary supply air will also bring a percentage of mandatory ventilation air (Outside Air).

Design and operation

Usually, there are either 2 or 4 pipes made of ABS, steel or copper that go through the floor. Functionally, according to the requirements of the use environment, it can achieve constant temperature and humidity or simply provide fresh air. After dust removal, dehumidification (or humidification), cooling (or heating) and other treatments, it is sent to the room through the fan, and the original air in the room is replaced when it enters the indoor space. Of course, the functions mentioned above must be determined according to the needs of the use environment.

The point-of-sale tools are downloadable documents to help aid you in conversations with customers making decisions about heating and cooling systems. 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. Before we get any deeper into this subject we need to cover the basics of zoning.

It’s just a mechanical device used to control the air flow of the duct.There is a actuator which is connected to the shaft of the damper.So we can control the airflow by varying the voltage of actuator. Therefore, to evaluate the real worthiness of an amount of money today after a given period of time, economic agents compound the amount of money at a given interest rate. Most actuarial calculations use the risk-free interest rate which corresponds the minimum guaranteed rate provided the bank’s saving account, for example. If one wants to compare their change in purchasing power, then they should use the real interest rate (nominal interest rate minus inflation rate). AC & Heating Connect was established to provide timely and accurate information about air conditioning and equipment, along with objective opinions and insight. This toolkit provides contractors with additional tools and insights for use on the job.

Cooling Mode

Fan coil units are an excellent delivery mechanism for hydronic chiller boiler systems in large residential and light commercial applications. In these applications the fan coil units are mounted in bathroom ceilings and can be used to provide unlimited comfort zones – with the ability to turn off unused areas of the structure to save energy. The fan motors within a fan coil unit are responsible for regulating the desired heating and cooling output of the unit. Some utilize an AC transformer, adjusting the taps to modulate the power supplied to the fan motor.

There are two main categories of pressure controls – high pressure and low pressure. These controls may be individual or combined into one control and are designed to protect the compressor. EAF air-conditioning exhaust fan is mainly used in the public areas of the floor, such as corridors, stair front rooms, etc. It refers to filter screens that meet the HEPA standard, with an efficiency of 99.998% for 0.1 microns and 0.3 microns. The characteristic of HEPA mesh is that air can pass through, but fine particles cannot pass through. It can remove more than 99.7% of particles with a diameter of 0.3 microns (1/200 of the hair diameter), and is the most effective filter medium for pollutants such as smoke, dust, and bacteria.

At present, air handling units mainly have several forms such as ceiling type, vertical type, horizontal type and combined type. Among them, the ceiling-type air handling unit is also called a hanging cabinet; the combined air handling unit is also called a combined air cabinet. A DOAS terminal is a fan-powered air terminal mounted in the ceiling plenum, with a chilled water cooling coil mounted at the inlet from the ceiling plenum. Heating coils (hot water or electric) are included in DOAS terminals which serve spaces requiring heat. Due to their simplicity, flexibility and easy maintenance, fan coil units can be more economical to install than ducted 100% fresh air systems (VAV) or central heating systems with air handling units or chilled beams. FCUs come in various configurations, including horizontal (ceiling-mounted) and vertical (floor-mounted) and can be used in a wide range of applications from small residential units to large commercial and industrial buildings.

In areas of the world where there are legally enforceable energy efficiency requirements for fan coils (such as the UK), DC Fan Coil Units are rapidly becoming the only choice. When I set the sub meter to measure the component performance, I found the heat pump loop is both heating and cooling the hotel instead of designed heating only, while the chilled water loop only cools the hotel during early morning. Since the heat pump cop (2.8) is lower than the chiller COP (5.1), the simulated results cannot reflect the design performance. In high-rise residential construction, typically each fan coil unit requires a rectangular through-penetration in the concrete slab on top of which it sits.

How a Variable Air Volume VAV System Works

As a result, the office equipped with VAV consumes overall 4% more electricity than the office with FCU. Corner spaces are often difficult to include with other spaces because they have two exposures. Looking at the image we can see that there are two cooling zones between corner spaces that are on the south exposure that could be grouped into one zone, Zone #5 below. The same is true for the two zones between corner spaces on the North exposures, Zone #2. If you had interior zones they would be separated from any exterior zone because interior zones are often exclusively in cooling mode due to internal heat gains and the lack of heat loss from any exterior surfaces. This is the miniature of the air handling units.It is operated by the cooling water.