What Are The Rooftop HVAC Units?

When rooftop units were first introduced some 40 years ago, they were considered by system designers and building owners to be a bare bones, low cost, simple solution to low-rise building HVAC needs. Low cost was the primary driving force for both manufacturers and users. But while they were popular with designers and owners, many maintenance managers considered them nightmares: difficult to service, prone to breakdowns, inadequately protected from the elements.

Today, everything has changed. Gone is the concept of one size fits all. Buyers have more options, including practically all of the same features found in other types of building HVAC systems, from economizers for energy conservation and prewired interfaces for building automation systems to heat wheels and other heat recovery devices. No longer can the systems be labeled as bare bones.

What has contributed to this change has been a shift in focus from first costs to life-cycle costs by both manufacturers and users. The result has been the development of new rooftop systems that include features to make them more efficient and easier to maintain.

The typical rooftop unit today comes in one of two configurations: single-zone or VAV. Single-zone systems remain the more widely used. They are low-pressure systems that provide a constant volume of airflow to a single zone controlled by a single thermostat. Since they do not include controls for multiple zones, this type of rooftop unit is best suited for use in the areas with fairly uniform heating and cooling loads.

The VAV configuration is gaining popularity, primarily as a result of its ability to serve multiple areas, each with different heating and cooling loads. The typical VAV rooftop unit supplies air at a constant temperature to a distribution system that includes VAV boxes to regulate airflow into each different area. The VAV configuration makes the units more flexible while improving their operating efficiency.

Rooftop units are available today in a wide range of capacities and configurations. The most common cooling configuration uses a DX system, with air or water cooling. Operating efficiencies for air-cooled units range between 1.0 and 1.5 kW per ton, and between 0.80 and 1.0 kW per ton for water-cooled units, including all fan and pump energy use. Units can also be configured to use externally generated chilled water. Today’s typical rooftop unit is 30 percent more efficient than those of earlier generations.

Rooftop units can use hot water, steam, natural gas or propane for heating, with capacities ranging from 40,000 to more than 2 million Btu for natural gas and propane units, and up to 4 million Btu for steam units.

Some of the most common complaints about rooftop units have come from maintenance personnel. Early generation systems simply were not easy to maintain. Access panels were held in place with sheet metal screws. Panels often were not replaced properly and screws were lost, exposing the interior of the unit to the elements. With time, the protective finishes on the exposed panels broke down, resulting in rusting and further exposure of unit components to the elements. Removable panels were often dropped during removal or reinstallation, resulting in damage to the building’s roof. But perhaps the most serious drawback was that the units were not designed to make maintenance easy. As a result, proper maintenance was rarely performed.

New rooftop unit designs facilitate maintenance. Exterior panels are protected by an epoxy finish that resists the elements, practically eliminating rusting problems. Machine screws have been replaced with hinged panels and latches, allowing easier access and more secure fastening of panels. Electronic diagnostic panels have been included in some system designs to ease system setup and troubleshooting. The net result is that rooftop systems offer the same advantages as earlier generation systems — including low first costs, factory assembly and ease of installation — without sacrificing performance or efficiency.

Rooftop units are suited for use in practically any low-rise application, such as in retail and institutional facilities. They are particularly well suited for applications where flexibility is required, such as frequent reconfiguration of interior spaces and functions.

Fresh Look At Ductless HVAC Systems

While many types of HVAC systems are advancing, some advances are overlooked because they have occurred in some of the less glamorous types of HVAC systems: rooftop units, split ductless systems and portable AC units. The result of these gains is that facility executives have more options today when it comes to selecting systems and components to meet building needs. But having more options is good only if the most appropriate option is selected for a particular application. Simply rushing into using new HVAC technology without first understanding the appropriateness of that technology for a given application is a recipe for disaster. Inappropriate system selection can result in poor IAQ, poor system performance, high energy use, increased user complaints and maintenance headaches.

Ductless HVAC Systems

Ductless HVAC systems, like rooftop systems, have been widely promoted by some for their low first costs and their ability to provide a quick and easy solution to building HVAC problems. And like rooftop units, they have been widely criticized by maintenance personnel as being difficult to maintain. Ductless HVAC systems, like all other HVAC systems, have their applications and their limitations. Properly applied, they can provide flexibility and improve comfort in a cost-effective way. Improperly applied, they can cause maintenance headaches, contribute to IAQ problems and cause comfort problems for building occupants.

Ductless HVAC systems come in a number of different configurations. Most are two- or four-pipe fan coil units that can provide both heating and cooling. More recently, units have been introduced that are essentially ductless heat pumps, with one portion of the unit mounted in the conditioned space, and the other mounted outside the facility.

The systems offer several advantages that go beyond low first costs. With no central air handler, less mechanical equipment space is required. Lower ceilings can be used since the units require no ductwork. With individual thermostats controlling each unit, spaces can be easily zoned. With all operating components, such as the fan, the thermostat, and the heating and cooling coils located in a single unit, modifications can be readily made to the HVAC system to match changes made in space configuration or use. For these reasons, split ductless systems are frequently found in educational and healthcare facilities, computer rooms, lobbies and building entryways.

The biggest drawback of ductless systems is their inability to supply the occupied space with fresh air. Some fan coil system designs did include a small outdoor air intake, but ongoing problems with the freezing of coils led many maintenance departments to block off these intakes. Split ductless systems do not supply the conditioned space with fresh air. Fresh air to these areas must be provided by a separate system.

Maintenance requirements are an important issue with ductless systems. Because the systems are so simple in their design, and the components so relatively small, maintenance requirements can easily be overlooked. But in spite of their simple design, ductless systems require regular maintenance. Filters must be changed. Condensate pans must be checked and cleaned. Fans and belts must be inspected. Controls must be tested. The problem for many maintenance managers is that the cost of performing the required maintenance may offset any cost advantage offered by the system. But overlooking the maintenance requirements will decrease system performance, shorten equipment life and adversely impact indoor air quality.

Nevertheless, there are good applications for ductless HVAC systems. Because each ductless unit is controlled by its own thermostat, conventional fan-coil-based ductless systems provide an unlimited level of zone control, ideal for applications where individual room control is required. Split ductless systems are also suitable for meeting the HVAC needs of spaces having unusually high cooling loads, such as rooms housing telecommunications or computer equipment.

HvacDepartment.com - Thermostats and Programmable Thermostats Information

Thermostats and Programmable Thermostats Information

Your thermostat or programmable thermostat is an integral part of your comfort system. These thermostats, whichever type you have, require little maintenance. Sometimes the only thing people know about their AC and Heating systems is how to turn the thermostat on and off and change the temperature setting.




A very common occurrence with service calls is the complaint that the thermostat isn't working properly. Sometimes this is true but most often it is something entirely different. Because some people believe the only problem with the system rests with the thermostat, they'll go down to the local hardware store and purchase a brand new thermostat. They get home and dust off the tool box, never read any directions, and proceed to change the thermostat. Some are successful and some are not. Those that are
most likely read some directions or had someone read the directions for them. The ones that are not successful end up calling a professional in to finish the job.





The bottom line advice to most people is to call a professional if something is wrong with your system. The problem may not be with the thermostat and you may exasperate the problem which will cost more in the long run. Additionally, If you have a multi-zone system, a high-efficiency heat pump or even just a heat pump, a regular split-system AC and a boiler for heat (and you have one thermostat), or an apollo based system (hot water heated in a water heater) with a split AC system, call a professional.
These systems can be very complex and may require special sub-bases so the control circuit will work properly. Additionally, for heat pumps, there are different controls, and wires for these controls run into the thermostat, they are multi-colored wires. These controls can be very complex and each wire must go to the correct terminal on the thermostat or the unit will not run correctly.





Additionally, be aware that thermostats are equipped with heating and cooling anticipators. Cooling anticipators are not adjustable where heat anticipators are adjustable in mechanical thermostats. Setting the heat anticipator is important for your heating system to function properly. It is set according to the amp draw on the control heating circuit. Make sure the heat anticipator is set properly so you will get the best out of your heating system.





Installing a New Thermostat




The first thing you should do before changing the thermostat is to select the proper thermostat for your system. If you are retired or if someone is at home most of the time during the day you most likely do not need a programmable thermostat. If this is the case the only benefit you will get from a programmable is at night. Once you have made the selection you can proceed to the next step.




Thermostat Installation Advisory: If you decide to install your own thermostat you do so at your own risk. There are many incidences where the homeowner installed their own thermostat and were successful. There are also many incidences were the homeowner was unsuccessful. The ones that were unsuccessful wasted part of their day, ruined a thermostat or two, and caused the malfunction of an integral part of their system. That is not mentioning the fact that they ended up calling a professional HVAC Technician
to fix the problems caused by improperly installing a thermostat. The ones that are unsuccessful end up paying three to four times what they would have paid had they called a professional in the first place. Factor this in to your decision and if there is any doubt call a professional to install the new thermostat.




* Get the tools together that you will need to do the job right. You will need:



o A small straight-slot (or flathead) screw driver

o A small phillips screw driver

o A pair of needle nose pliers

o A utility knife or wire strippers (for small wire)

o Plastic wall anchors (sometimes provided with the thermostat)

o A drill with a bit to make the holes for the plastic wall anchors

o A small level

o Two pencils or pens

o A small paper bag and some masking tape (tape the bag below the area where the thermostat is so that any trash or dust will fall into the bag and not onto the floor)

o Some touch up paint

o Clean hands (don't do a great job changing the thermostat and leave all those prints all over the wall)

o Plenty of light




* Turn the power off to the unit at the circuit breaker or the emergency cutoff switch. After doing that make sure the power is off by turning the thermostat to the on position and going to the unit to make sure it is not on. Not all circuit breakers are labeled correctly and not all emergency switches are hooked up. Just make double sure that you have killed power to the unit not only for your safety but also to keep from blowing the transformer.



* Pull the cover off the front of the thermostat. If it is a mechanical thermostat there should be a little adjuster tab in the center of it. This is your heat anticipator. It should have numbers ranging from 1.5 to .1. Take note of this setting and remember to set the new thermostat to this same setting if you are replacing a mechanical thermostat with another mechanical thermostat. You probably want to do this now before you proceed further. If you are replacing a mechanical with a digital, the digital
should set itself automatically. If not read the instructions on the new thermostat for instructions on how to set the anticipator. This is very important. An improperly set anticipator will cause your heater to run improperly. The thermostat is also equipped with a cooling anticipator. Cooling anticipators are most often on the sub-base and are non-adjustable.



* Unscrew the thermostat from the sub-base. Take note of each wire. The following list should match the wires and terminals on your thermostat.



o Red to the RH or RC terminal with a jumper wire between RH and RC. Or Red to the R terminal which is shared with both the heating and cooling. It has an internal jumper built in to the sub-base. The red wire is the hot wire. All other wires are common wires.

o Green to the G terminal. This is for the fan.

o Yellow to the Y terminal. This is for air conditioning.

o White to the W terminal. This is for heating.

These are the four wires that you need to control the heat, cooling and the fan. If the colors of the wires do not match the colors described here make sure you mark the wires with masking tape. If there are more wires that are not hooked up don't worry. This is common. Thermostat wire comes in many different varieties and the contractor who installed the system probably used 5 wire or 8 wire thermostat wire. They used what they needed and simply twisted or cut the other wires off.



* Remove the wires from the terminals on the sub-base. The power should be off so you shouldn't have to worry about being shocked. Be careful not to let the wires fall back into the wall. Sometimes there is just enough wire to reach the terminals and that's it. Try pulling the wires a bit to see if there is more wire behind the wall. Most of the time there is some slack and you can pull the wire out more. Unscrew the sub-base from the wall while holding the wires. When you get the sub-base off wrap the
wires around the pencil or pen. This will keep the wires from falling back into the wall.




* Get the new sub-base and compare it to the old one. Hold it up to the wall in the position you want it. Is the old paint that was covered by the old sub-base going to be covered by the new sub-base? If any of the old paint is going to show you may want to make some touch ups now. After finishing with that, put the new sub-base back on the wall in the position you want it. Make sure it is as level as possible. You can use a level to do this. (This is very important especially for mechanical thermostats.
It must be level or the mercury switch will not keep the proper temperature settings in the house. Make sure it is level.) Mark the new holes through the sub-base where the screws will go into the wall to fasten the sub-base.



* It is important in this step to have the proper drill bit size for the size of wall anchors you have. Some wall anchor kits come with a bit in them. We recommend the wall anchor kits with the bits in them because it is the perfect size drill bit for the anchors. The bit should be slightly smaller than the anchor. If the bit is bigger the wall anchor will not hold and the possibility exists that the thermostat will fall off the wall. Drill the mounting holes you made for mounting the sub-base. Insert
the wall anchors and push them hard with your thumb. Approximately 1/16th of an inch on the lip of the anchor will remain sticking out of the hole. If it is more than that use the butt-end of the screw driver and push it in until just the lip of the anchor remains visible.



* Undo the wires from the pencil or pen and run them through the center of the sub-base. Insert the screws and screw them only snug tight. Get the level and make sure the sub-base is level. When you are sure that it is level, tighten the screws. Be careful not to allow the sub-base to move when you are tightening the screws.



* Using the color code of the wires (or if they didn't match, the color markings you made with masking tape), attach each wire to their proper terminal. Some people like to loop the wire around the terminal screws. This is not necessary. What is necessary is that the wires are attached to the terminals and they are tight. Additionally, make sure that none of the bare wire is touching anything except the terminal. Once the wires are attached you are almost finished completing the task of installing the
thermostat. The hard part is over!



* Attach the thermostat to the sub-base. The screws for this are built in the the thermostat. Tighten these screws and check to make sure the heat anticipator is set to the same setting as the old anticipator setting.


* Attach the front cover to the thermostat and restore power. Start and check the heating, air conditioning, and with the heating and air conditioning off, the fan only sequence. All systems should be working properly at this time (if you did the task properly) and you are the proud owner of a brand new, properly installed thermostat.





Programmable Thermostats




Programmable thermostats can save you more than ten percent on your homes utility bills. For that reason a programmable can pay for itself within a few years depending on the type and expense of the type you purchase. Among others, you can expect good quality from Honeywell products. If you are or someone else is at home most of the day and night, you most likely do not need a programmable. Programmables are designed for the family on a regular schedule. Those that wake at a certain time, leave the
home at a certain time, return at a certain time, and go to bed at a certain time (on a regular basis), will benefit from a programmable thermostat. Read the following information and see if it applies to you for your benefit.
How the programmable thermostat works




You have four settings on the programmable thermostat.


* Wake - this is the setting you want the temperature to be at when you wake. If you wake at 6 a.m. you probably want to set the wake time and temperature for 5:30 a.m. and whatever the desired temperature is for you.

* Leave - this is the time the last person leaves the home for the day. If that person usually leaves at 8 a.m. then the thermostat can be set to change the temperature at 7:30 a.m.

* Return - this is the time that the first person arrives home for the day. If that person arrives home at 4 p.m. then the time and temperature can be set at 3:30 p.m. That way when the person arrives home, the home is at the desired temperature.

* Sleep - this is the time when everyone goes to bed for the night. If everyone is in bed by 10:00 p.m. then the thermostat can be set to change the temperature to a lower setting for the night.




Most programmable thermostats have settings for both the weekdays and weekends so on Saturday and Sunday you can tailor the settings according to your comfort level and usual schedule for those days. All of them have options to over-ride the program for manual settings and an additional benefit to owning a programmable is that most are equipped with a compressor delay to protect your compressor from short cycling.