2Packaged HVAC Equipment Is the most common source for HVAC in small to medium commercial buildingsUsed in:Retail StoresSupermarketsRestaurants
3Packaged HVAC Equipment Rooftop units, better known as RTUs, are popular because they are the "least cost solution" to heating, ventilating, and air conditioning a building.
4Rooftop Units Some of the reasons for this are: RTUs are unitary or packaged equipment and require no field refrigerant piping.RTUs provide heating, cooling, air moving, outside air introduction, and a filtration system.RTUs do not take up valuable floor space.RTU service time is reduced because all of the components are together.Routine service does not interfere with store operation.RTU replacement is quicker and doesn't interfere with store operation.
5Types of Rooftop Units: Multi-zoneVAV (Variable Air Volume)Constant Volume
6Multi-zoneThese systems are still available but are losing favor because of their inherent energy inefficiency.A multi-zone unit typically consists of a hot and a cold deck.There are also three deck units, the third being the bypass deck.This is more efficient because you add hot or cold air to the return air.Some additional disadvantages are:You are limited to the number of zones available and the need to distribute the air proportioned to each zone evenly.Building energy codes place restrictions on the use of reheat temperature control.
7VAV (Variable Air Volume) These systems are becoming more popular for their ability to provide unlimited zoning control and ease of future reconfiguration of space and zones.VAV systems are available in the 15-ton and up range in cooling only or cooling with heat versions.The heating section allows for morning space warm-up and building temperature setback.
8Constant VolumeMost retail outlet stores have RTUs with a single-zone heating and cooling configuration.These units have constant air volume to a single zone with a single thermostat controlling them.They are the least expensive to purchase and are the simplest to install and maintain.
9Roof Top UnitsA typical RTU is a manufactured piece of equipment that is factory-assembled, delivered to the site in one piece and ready to operate with a single-point control interface.In most cases, they connect to utilities such as natural gas and electric power.In some configurations, they can be connected to a system’s hot water or steam system for heating, and chilled water system for cooling.In most cases, each unit is factory-tested to insure quality control.Having said this, it is still very important that a responsible contractor perform the start-up or commissioning service.
10Roof Top Units Check operation of heating and cooling. The following points are essential parts of commissioning:Check operation of heating and cooling.Adjust the air/fuel mixture for your altitude.Adjust belts.Tighten bolts, particularly in the blower section.Remove shipping braces.Check for refrigerant leaks.
11Construction and Installation Rooftop units are constructed of galvanized steel with a primer and a final UV-resistant paint coat.The exterior panels are insulated with glass fiber with a thickness of 1- to 2- inches.Units being manufactured with a solid metal liner are becoming more common due to IAQ (Indoor Air Quality) concerns.
12Construction and Installation Condensate drain pans are constructed using steel with a mastic coating, galvanized steel, PVC, or stainless steel.Deeper pans with two-way sloping to drain are desirable to remove condensate from the unit completely and prevent ponding of water, where algae and microbial will proliferate and reduce air quality.
13Construction and Installation An RTU mounts on a curb, which is a perimeter frame that supports the unit off of the roof deck.The top of the curb has a mating flange that adapts to the RTU. When you are replacing an RTU with another one having a different footprint, it is common to use an "Adapt-a-Curb".This device adapts the new RTU to the existing curb. Properly manufactured and installed with gaskets, the Adapt-a-Curb is an acceptable way to install a replacement RTU while not disturbing the existing roofing.Ductwork connections and gravity are usually not enough to keep an RTU in place during high winds. Straps, sheet metal screws or welding are common ways of fastening the RTU to the curb.
14Construction and Installation RTUs should be placed near the area where they will heat or cool.This saves ductwork installation and thermal duct losses. Location relative to exhaust air fans or vents, plumbing vents, and process exhaust, such as kitchen hoods, should be taken into account.Additionally, ambient, prevailing wind conditions affect movement of air on the roof into the outside air intake louvers.Wind conditions also affect the operation of the condenser fans. When not energized, the fans can begin freewheeling or wind milling due to wind.
15Construction and Installation Single-speed motors, when started, want to continue in the direction the fan was freewheeling.This could block air movement through the condensing unit. A three-phase unit will only run in one direction without changing electrical connections.If freewheeling in the wrong direction when energized, the fan will draw additional amperage and possibly damage the motor, fan blades, and or the fan supports.
16Construction and Installation The architect, roofing consultants, and engineer should consider access to rooftop equipment in building design.Wear or walk pads to the units can minimize future damage to the roof by individuals and service equipment.With all of the choices available in RTUs today, there is sure to be something that will fit your needs.Discuss the options with your HVAC provider and, after considering all of the options, pick the one that will satisfy your needs.
17Packaged HVAC Equipment In 2000 the U.S. Department of Energy estimates that rooftops and unitary air-conditioning equipment accounts for 62% of total energy consumption for cooling commercial buildings.
18Service and Maintenance of Packaged HVAC Equipment Packaged equipment is :Smaller in sizeMore numerous in numberUsually not as well maintained
19Why are they not as well maintained? Out of sight out of mind!Often ignored and forgotten until they have degraded to a point of failure.Effects of failure are limited to small number served.Large buildings have so many that preventive maintenance would require a lot of a service technicians time.In many cases the unit is all contained within the unit. i.e. – no chiller, no pumps, no additional piping, and no separate refrigerant piping.