Control in a particular zone is limited to what the system is currently set (i.e., cooling or heating).Rooftop installation costs are low to moderate, but operating costs are typically 50% higher than water-source heat pumps. Additionally, the systems are exposed to the elements and are subject to damage and vandalism. These options provide a good opportunity to save energy by reducing the fan speed and possibly increasing the supply air temperature in small increments with continuous polling. The idea of zoning is to breakdown large areas of a building into smaller zones with similar load profiles. When a zone on the south facing portion of a building is calling for maximum cooling, the north facing zones may be in minimum cooling or heating mode. Zoning allows different spaces the ability to provide cooling or heating and vary the flow (CFM) depending on the demand of that zone’s temperature sensor.

1. A concealed fan coil unit will typically be installed within an accessible ceiling void or services zone.
2. Water-source and geothermal heat pump systems are the most energy, cost, and space efficient of any system in the industry.
3. • Because the entering chilled water temperature must be several degrees above the space dew point, the water side delta T is generally significantly lower than a fan coil unit or variable volume air handling unit delta T.

This pressure change is picked up by a static pressure sensor in the main supply air duct. The air handler will deliver a constant temperature of 55ºF (13 ºC) supply air to the VAV boxes. While the supply air temperature stays constant the volume (CFM) of air will vary based on the total demand of all the zones on the system. There are several control strategies to adjust the speed of the fan which we’ll discuss below. To model the air cooled heat pump as heating source for hotel, I modelled 2-pipe heat pump loop at water-side and set it as the heating source at air-side (cooling source as chilled water loop). The loop operation is set as snap with the snap temp as mean temp of indoor heating and cooling design temperature (otherwise much unmet hour occur).

It has been widely used in high-clean places such as operating rooms, animal laboratories, crystal experiments and aviation. When the VAV boxes are connected to a building automation system that monitors the function and status of the boxes there are various options for control. As you can see in the diagram above the VAV Damper goes from a minimum of 30% open, whatever the minimum required to meet ASHRAE 62, all the way to the damper being 100% open. These motors are sometimes called DC motors, sometimes EC motors and occasionally EC/DC motors. On the other hand FCU is the equipment used to condition the space it can either be a DX or Chilled water system. Where r is the annual rate, i the periodic rate, and n the number of compounding periods per year.

When the temperature sensor in the space calls for cooling it sends a command to the VAV box controller which then adjust the supply air flow rate (CFM). The adjustment is done by an actuator rotating the VAV box inlet damper either open or closed in increments. Variable air volume is more energy efficient than constant volume flow because of the reduction in fan motor energy due to reducing fan speed (RPM) at partial load. As the cooling or heating demand is reduced because of a mild temperature day, the VAV Air Handler system can reduce the amount of air flow (CFM) by reducing the fan speed.

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Vav with FCU

For a single VAV air handler that serves multiple thermal zones, the flow rate to each zone must be varied as well. The VAV box regulates the flow (CFM) to a zone in relationship to the demand of the temperature sensor in the space. In high-rise buildings, fan coils may be vertically stacked, located one above the other from floor to floor and all interconnected by the same piping loop. Fan coil units linked to ducted split air conditioning units use refrigerant in the cooling coil instead of chilled coolant and linked to a large condenser unit instead of a chiller. They might also be linked to liquid-cooled condenser units which use an intermediate coolant to cool the condenser using cooling towers.

A concealed fan coil unit will typically be installed within an accessible ceiling void or services zone. It is quite common for the return air not to be ducted and to use the ceiling void as a return air plenum. On the other hand, because the central air handling unit provides all cooling to the spaces, it is required to move a much greater volume of air. Thus, the floor space required for air handling equipment and vertical duct risers (shafts) is much more significant when compared to the other systems. The heating hot water valve will modulate open providing a range of heating hot water flow (GPM) to meet the heating load.

The fan filter unit is a terminal purification equipment that combines a fan and a filter (high-efficiency filter (HEPA) or ultra-high-efficiency filter (ULPA)) to form its own power. To be precise, it is a modular terminal air supply device with its own power and filtering function. The fan sucks air from the top of the FFU and filters it through HEPA, and the filtered clean air is evenly sent out at the wind speed of 0.45m/s±20% on the entire air outlet surface. In this instance, the only real difference would be that the air handling unit operates by bringing in fresh air from the outside, whilst the FCU generally recirculates and conditions the air in the space it serves. The high side being the main supply duct from the air handler to the inlet of each VAV box. The main is considered upstream of the VAV box, while downstream of the box is considered the low-side supply.

• VAV systems are very cost effective from a chilled-water and heating-water-pumping perspective. Because the unit transfers heat to the space using forced convection, the coil heat transfer area required is reduced as compared to a chilled beam. The reduction in coil heat transfer surface area results in lower coil water side pressure drop and lower pumping energy. Forced convection heat transfer also yields higher water side delta T which also results in lower pumping energy.

Ventilation ASHRAE 62

Fan coil systems are comprised of water-to-air coil air handlers connected via a two or four-pipe insulated water loop. Fan coils require complex chillers and boilers to provide water loop fluid in a particular temperature range (i.e., chilled water for cooling and hot water for heating). Two-pipe fan coils have a major disadvantage as control is substantially limited to whatever mode the system is currently set at (i.e., cooling or heating). A four-pipe version can be installed that requires both chilled and heated water to be available at the same time.

Variable air volume

• To prevent condensation at the DOAS terminals during morning start-up, humidity control during unoccupied building hours is required during the cooling season. VAV systems typically have a higher first cost than water-source heat pumps, and may have similar operating costs, resulting in overall increased life cycle costs. Fan coil units may be connected to piping networks using various topology designs, such as “direct return”, https://1investing.in/ “reverse return”, or “series decoupled”. The output from an FCU can be established by looking at the temperature of the air entering the unit and the temperature of the air leaving the unit, coupled with the volume of air being moved through the unit. This is a simplistic statement, and there is further reading on sensible heat ratios and the specific heat capacity of air, both of which have an effect on thermal performance.

FCUs are commonly used in HVAC systems of residential, commercial, and industrial buildings that use ducted split air conditioning or with central plant cooling. FCUs are typically connected to ductwork and a thermostat to regulate the temperature of one or more spaces and to assist the main air handling unit for each space if used with chillers. The thermostat controls the fan speed and/or the flow of water or refrigerant to the heat exchanger using a control valve.

Variable Air Volume, or VAV, is one of the most common types of HVAC systems used in large commercial buildings today. A typical system is usually comprised of a large air handler, central vav vs fcu ductwork system, and a relatively large equipment room. Conditioned air is distributed throughout the building via a central ductwork system and is regulated via dampers in each space.

Alternatively a condensate pump may be employed where space for such gravity pipework is limited. Water-source and geothermal heat pump systems are comprised of individual packaged units that transfer heat via a single- or two-pipe water loop. Each unit can be used in either heating or cooling mode year-round and loop temperature is maintained via a boiler/tower combination or earth-coupled loop. Each zone has complete control of its heating/cooling mode and each unit is independent from the others.

I suspected before that higher fan power of VAV results in more temperature increase through fan and hence more space cooling requirement. But after manually change the delta T through fan, the effect is not very obvious that the space cooling increase proportion drops from 32% to around 28%.seems it is not the main cause. Lately I am modelling an office & hotel complex through eQUEST with energy conservative strategies added one by one to test the energy saving effect.

During cooling mode, the Variable Air Volume VAV box will modulate between a minimum CFM setpoint and the calculated design maximum cooling CFM setpoint based on the zones peak cooling demand. • Because the entering chilled water temperature must be several degrees above the space dew point, the water side delta T is generally significantly lower than a fan coil unit or variable volume air handling unit delta T. This results in increased pumping energy for the DOAS terminal system when compared to a fan coil unit system or variable air volume system. The fan coil unit will contain a purpose designed drip tray with drain connection for this purpose. The simplest means to drain the condensate from multiple fan coil units will be by a network of pipework laid to falls to a suitable point.

Thus, the airside delta T is reduced and greater design airflows are required in the building spaces. This results in higher fan energy, increased fan noise and increased ceiling space requirements. Rooftop systems are similar to VAV systems in that they use a central ductwork system to distribute conditioned air into the building space. However, instead of one central unit, the system is comprised of multiple units which can be tasked for different conditioning requirements. Rooftop systems usually require additional structural re-enforcement, as well as cranes or other lifting equipment, to place the units.