Avoiding Costly Mistakes in Light Commercial HVAC System Design

Avoiding Costly Mistakes in Light Commercial HVAC System Design

While residential and commercial HVAC system requirements are similar, there are defined differences that residential builders who are venturing into light commercial construction need to know about so they can avoid making potentially costly mistakes.

Basically, unlike residential construction where windows help ventilate a home, commercial construction does not rely on windows for ventilation. Instead, the outside air, general exhaust, toilet exhaust and process exhaust must be provided by — and specifically calculated for — commercial HVAC mechanical systems.

So, in addition to the heating and cooling calculations needed in residential construction, builders must also add newly introduced outside air to their commercial calculations.

This additional requirement necessitates that residential builders select and install commercial-grade mechanical components rather than install what they typically use in new homes.

Elements Common to Light Commercial Systems

To help familiarize residential builders with the differences in commercial systems, we have compiled a list of elements that are common to light construction systems that are not found in residential systems.

These elements apply specifically to buildings up to two stories high. While the basic principles are the same for systems used in larger commercial buildings, the configurations for systems in large and small buildings differ completely.

Roof Top Units – Heat, Cool, and Provide Outside Air


HVAC rooftop mechanical units provide the heating, cooling and most ventilation requirements for light commercial spaces. Essentially, they are the workhorses of light commercial construction. 

A rooftop unit is generally a factory “catalog made to order” assembly that includes a condenser and an expansion coil for cooling, a heat source and a single fan for forced air heating and an intake opening for outside air. 

The fuel heat flue discharges on the side of the unit.


Power Wiring – Complex and Expensive

Power wiring varies depending upon the size of the HVAC unit. 

 Units up to three tons can be powered by 120 volts, 208 volts or 240 volts. The most common units — those seven tons to 15 tons and larger — can be powered by 208 volts, 240 volts or 480 volts. 

Power is supplied through a disconnect mounted on the side of the unit. Frequently, a 120-volt convenience receptacle for servicing the unit is either included with the unit or installed in the field. 

Larger units may require a custom-ordered disconnect, which can be expensive. 

Also, keep in mind that, for the largest units, breakers in the panel are not sufficient circuit protection. For greater protection, you will be required to alter the electrical service gear for the entire building.


Outside Air Control – Economizers or Power Exhausts


Outside air control can be improved with an “economizer” — a modulating damper that senses the outside air temperature and increases the intake air up to 100% in order to provide free cooling when possible. 

A power exhaust can be, but seldom is, added as an option to a rooftop unit. Independent general and toilet exhaust systems are usually more cost-effective. 

If a power exhaust is added, however, a barometric relief valve on the rooftop unit will be required so that the outside air injected by the system does not excessively pressurize the building.


Zone Control – Not Always Needed

Commercial buildings with larger spaces, more rooms or uneven or non-uniform window placements have a greater heating and cooling load, which makes zone control in this type of space more important. 

In smaller strip shopping centers spaces of about 1,500 square feet where a single zone can be used, builders should not use forced air. 

However, if a tenant in a strip center has combined multiple spaces, builders can configure the ductwork from each single zone rooftop unit to provide interior and exterior zones. 

For the next level of improvement — spaces requiring six to about 12 zones — builders should add zone control devices in the ductwork. Here, the unit discharges air at a specified temperature, and zone dampers in the ductwork modulate the air volume for temperature control. 

When zone dampers are used, each mechanical unit must have a bypass damper to short-circuit the supply air to the return in order to relieve pressure caused when dampers restrict all the airflow at the same time. Such a system also requires that a system controller coordinate the unit and devices. 

In colder climates, builders frequently add radiant heating near windows and in vestibules to supplement the heating in these zones. In the past, builders used electric reheats in the ducts, but most energy conservation codes are restricting or prohibiting using these coils in order to avoid cooling and then reheating the same air.


Avoid Common Errors Along the Way

In addition to understanding the fundamental differences between residential and commercial HVAC systems, residential builders considering diversifying into light commercial construction should avoid the following common errors when installing commercial systems:

  1. Don’t use residential systems for commercial projects. Residential HVAC systems are not designed for, nor capable of, providing the outside air required by code and therefore have no place in commercial structures.
  2. Outside air intakes should be included when installing RTUs. RTUs without outside air intakes are suitable for cooling a warehouse, but not an occupied building.
  3. Don’t forget about general exhaust. Once you have chosen the exhaust required by code for your building, include appropriate compensating features such as a barometric relief valve, so that the entire system work in concert.
  4. Roof alterations are tricky, can be costly, and must be managed. 

More and more commercial flat roofs are proprietary systems that specify exactly how each roof curb and penetration must be configured in order to maintain its warranty, so builders shouldn’t simply poke through the roof and then caulk the penetration with roofing cement. 

Also, since curbs and roofing are both set on the deck, the curb height must include the thickness of the roofing with insulation as well as the required height above the top of the roofing. If the roof slopes more that 2% (1/4-inch in 1 foot) the curb must be altered to keep the top level.  

With proprietary systems, builders must use portals to accommodate the control wiring, power wiring and gas piping. In addition, they will need to have a factory-certified technician make all roofing patches.
  5. Metal roofs may require structural reinforcement. Metal roof structures are designed to accommodate only a little extra load, so installing additional rooftop units may require structural reinforcing. 

One common solution when working with metal roofs is to place the compressor-side of the new rooftop unit — the heavy end — over a beam. The installation may also require that you have angle iron reinforcing the joist web. 

In some municipalities, any additional structural work must be designed by a structural engineer or architect.
  6. Zoning is important for customer satisfaction. 
The opportunities for zoning in the smallest of commercial structures are limited, as described above. However, keep in mind that the customer may want to you to make some attempt at zone control or he may think that the building’s heating and cooling just doesn’t work correctly.
  7. Disconnects become more costly and tricky to order. For the smallest rooftops 
the disconnects needed are similar to those in residential construction. However, as the unit size increases, the requirements and costs of disconnects change dramatically. 

That’s because in commercial construction disconnects must be specifically selected for their characteristics and over-current protection. Either the electrical or HVAC contractor can provide disconnects, but builders should be sure that the disconnects are the correct ones for the job. Depending on their characteristics, they can increase costs substantially and take valuable construction time if they need to be replaced.
  8. Forgetting to install service receptacles and/or lights can be expensive. A 120-volt service receptacle is generally advisable — and frequently required by code — for each rooftop unit. Builders can either purchase the service receptacle as an option with the HVAC unit or field-install it separately when installing the unit. 

What builders don’t want to do, however, is overlook adding a service receptacle after installing the unit. Inspectors will notice that the service receptable is missing during final inspection — and that will cost you time and money.

Plan an Entire Building System, Not Piecemeal Installations

Ordering and installing all the rooftop units needed for a building is a complicated task that requires planning the entire building system, not simply installing each HVAC rooftop unit as needed. The pointers above can help you achieve satisfactory, and cost-effective, results.

Improper planning, on the other hand, can leave you with a very costly solution you may not be able to ignore — tearing off the roof unit and buying a new one.

Also, don’t be overwhelmed if you find that your system requires a factory-certified installer to install it. Acquiring the certification is usually as simple as having your installer attend a free seminar provided by the factory.


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Carbon Monoxide – The Silent Killer

Carbon monoxide (CO) is a colorless, odorless, tasteless gas that is produced by the incomplete combustion of fuels such as wood, natural gas, gasoline, diesel, kerosene, coal and charcoal. It is caused by lack of oxygen or a disruption in the burning process.

Household appliances such as your furnace, water heater, stove, space heaters, charcoal grill and gas dryer can be sources of carbon monoxide, especially if they are not in good working condition or have been installed improperly. Vehicle exhaust fumes from attached garages, as well as improperly operating fireplaces, also can become carbon monoxide hazards, particularly if your home is well-sealed for energy efficiency.

Carbon monoxide can be an invisible threat to your family’s health and safety. Though more commonly associated with fires and automobile emissions, carbon monoxide poisoning can accumulate in any home unless certain precautions are taken.

Unfortunately, the symptoms are easily overlooked because they are often flulike. With mild exposure, most people experience headaches, fatigue and nausea. Medium exposure can cause a severe throbbing headache, drowsiness, disorientation, confusion and an accelerated heart rate. Extreme exposure can lead to unconsciousness, convulsions, cardiorespiratory failure, coma and possibly death.

It is important to schedule annual maintenance visits by a qualified technician to make sure all combustion appliances are operating properly and all chimneys and vents are free from obstruction.

The best method of detection is to use a carbon monoxide detector in your home. A carbon monoxide detector is a device very similar to a smoke alarm. It monitors the air for carbon monoxide and sounds an alarm if a specific level is detected. Ideally, you should have one detector adjacent to every living area in your home.

Carbon monoxide detectors are most effective when used in combination with preventive maintenance. For more information on how to schedule regular maintenance for your furnace or about purchasing a carbon monoxide detector, contact your local Accurate Air office.

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Broken Air Conditioner? Try These Steps Before Calling Us – And Maybe Save Some Cash

When your air conditioning system fails, Murphy’s Law states that it will be on the hottest day of the year. Before you call us, here are a few troubleshooting tips that might get you back up and running. While there are problems only a professional can fix, it may just be a simple problem that’s causing the malfunction, particularly if your system is relatively new and has not had any issues in the past.Equity Residential

1. Set your thermostat to the lowest possible temperature then set it well above the current room temperature. Listen for the system to turn off. If it does not, there are two possibilities — the breakers or fuses have blown, or the thermostat may be malfunctioning.

2. Check the breakers or fuses for the air conditioning unit. For a breaker box, open the panel up and check to see if any of the breakers have tripped to the “off” position. Move these back to the “on” position, and have someone else turn the temperature to below room temperature. If the breaker throws again while you’re standing there, there may be an electrical issue with the air conditioner. If you have fuses, these will typically be located in a fuse box outside, next to the unit. Turn the fuse switch to the off position, then examine the fuses. If any appear burnt, or if they make a noise when you shake them, replace the fuses. Turn the switch back to the on position and then turn the thermostat to a temperature below room temperature.

3. Check the air flow to the system. Blocked air flow is a common reason why air conditioners suddenly quit working. Go outside and check around the unit. If there are weeds or grass around it, trim these away and try the unit again. If the filter in the inside unit has not been changed in a while, take it out of the unit, then turn the system back on.  Don’t forget to replace the filter with another – pleated are best.

4. Examine the unit for any visible signs of problems. If all of the above steps have failed and your unit still will not function, look for issues such as ice build-up inside the indoor unit, water leaking from the unit, or oil that has spilled from the outside unit’s casing. These are signs that you will need to contact us.

While a general HVAC company can typically solve any issues you’re experiencing, if your system is still under warranty, you definitely want to pick the right company so that you don’t void your warranty.

Check with online review services, such as Angie’s List, to get an idea of the ratings for the residential HVAC companies in your area. You can also check with the Better Business Bureau, or ask your friends in the neighborhood who they have worked with in the past. In larger areas, you can also use Google maps or places app to get reviews of local companies. These can be very useful in narrowing your search.

Keep in mind that on severely hot days or stretches where the weather is very hot, you may not be able to get a service tech out to your location immediately. If you or someone in the home has health issues that could be worsened by high temperatures, let the residential HVAC company know — they’ll make an extra effort to get you taken care of.

Are you having trouble with your air conditioner? Have you tried these troubleshooting tips?

If your having trouble with your air conditioner tell us if you’ve tried any of these troubleshooting tips. In the comments below tell us about your experience.

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6 Tips For Keeping Buildings More Comfortable And More Efficient This Winter

The winter season is unpredictable, and nobody knows what frigid weather may be coming in 2013-14. Accurate Air is pleased to offer a short list of tips for commercial building owners and operators to help them save on their energy bills this season.

Here are Accurate Air’s six tips for keeping buildings more comfortable and more efficient this winter:

1. Inspect each HVAC system: Clean and perform regular maintenance to keep systems running more efficiently. Scheduled maintenance will keep equipment running smoothly and also keep utility bills down. Filter changes are a must: in addition to protecting the equipment, it will improved efficiency and indoor air quality while reducing repair costs. Also check drive belts for wear and proper tension to prevent frozen coils or a reduction in airflow.

2. Seal air leaks: Make sure that windows and ducts are properly sealed to prevent heat loss. Keep heat in by caulking, insulating, and applying weather strips to doors and windows.

3. Standardize indoor temperature: Put an end to the thermostat wars by determining the most effective standard indoor temperature and assigning one person to control it. A popular alternative is to use a remote sensor located in the space which cannot be tampered with. The thermostat can be located in an office or secure area and will now control the space from signals sent by the sensor.  Or consider adding lock-boxes for each thermostat or adding a remote monitoring service and letting someone else control it.

4. Prevent equipment freezing: Identify equipment that is vulnerable to freezing and prepare it for cold weather with proper drainage and/or freeze protection.  Hot water baseboard and radiant systems may have anti-freeze added to alleviate concerns of freezing pipes if the facility is left unattended on long weekends or shutdowns of extended periods of time.

5. Review building automation systems data: Utilize data from the building automation system to measure all mechanical systems’ performance, and make repairs when equipment performance drifts out of an acceptable range.

“The winter season presents a unique set of challenges, with everything from warm spells to freezing temperatures,” said Jack Wildt, service manager of Accurate Air. “Consistent maintenance and ongoing modifications help owners and facility managers identify problems quickly and save costs in the long term.”

Are you prepared for the upcoming winter season? Have you tried any of these helpful tips to help save on energy bills?

In the comments below tell if your looking to cut down on energy costs. Tell us how you’re preparing for this upcoming winter season.

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