#DOAS Archives - United CoolAir

February 4, 2022 by Matt Hanson

Packaged HVAC Indoor vs Outdoor

There are two basic types of HVAC systems, that being packaged and split systems. In short, a split system model contains a condenser and compressor residing in an outdoor cabinet while connected to an indoor evaporator. They connection by copper tubing and include various line lengths depending on numerous factors. Packaged systems on the other hand also known as all-in-one or self-contained are not as easily defined. Therefore, packaged HVAC indoor vs outdoor requires further explanation.

In a packaged HVAC system, all of the components; condenser, compressor, and evaporator reside in the same cabinet. However, there is a misconception about where a packaged unit is located. Some believe a packaged unit is located outside much like the condenser of a split system. So, when comparing a packaged system to a split system many HVAC providers will list the pros and cons each system.

HVAC installers will correctly point to the ease of installation and servicing of packaged units. However, they will also state that packaged unit installation is outside making them susceptible to weather, animal damage and rust. While this may be true of most packaged units on the market, there exist packaged units installed entirely indoors. For this reason, there are multiple reasons to consider HVAC indoor vs outdoor in a packaged unit.

United CoolAir Packaged HVAC Units

While split HVAC systems dominate the commercial HVAC industry, packaged units are often the right solution for many installations. For decades United CoolAir (UCA) packaged units have solved challenging HVAC installations. This is due to the fact of UCA units easy installation. Besides, these units also avoid any of the drawbacks of other packaged units on the market.

United CoolAir packaged units are modular with each module able to fit through a standard doorway as well as hallways. The use of quick connects means installations happen faster than many other brands. UCA units are also pre-charged and tested before shipment from the factory. As a result, we say United CoolAir units are All-indoor Solutions.

December 29, 2021 by Matt Hanson

Improving Indoor air hygiene

Since the onset of the novel corona virus that has become a pandemic, there is emphasis placed on improving indoor hygiene. People across the globe now realize that prevention of illness needs to be part of the strategy to control infection. Although mask wearing and social distancing may reduce transmission it is not enough to solve the problem.

Keeping building occupants healthy begins with making sure we are combating indoor air pollution. The Environmental Protection Agency (EPA) recommends fresh air standards for commercial buildings. Probably due to the fact the average American spends up to 90% of their time indoors and the workplace is one such instance.

To ensure fresh air is at satisfactory levels the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Standard 62.1 has established guidelines. These guidelines give building or facility managers a baseline for acceptable Indoor Air Quality and ventilation.

Identifying pollutants

Besides Corona there are other airborne pathogens that contribute to poor health. Indoor pollutant includes microorganisms, germs, spores, molds along with carbon dioxide and carbon monoxide. Since many pollutants have no smell and cannot visibility they can be potentially dangerous.

Combined together these variables come together to make indoor space unhealthy hence the term sick building syndrome. During the Summer of 1976 a new ailment named Legionaries disease during a convention of the American Legion in Philadelphia, PA. This was due to a strain of bacteria called Legionella found in the cooling tower of the AC system.

Symptoms of poor Indoor air

When buildings contain too much humidity people will describe them as being muggy. Then symptoms such as congestion, dizziness, fatigue, nausea along with irritation of the eyes nose and throat can set in. However, many of these problems can be identical to a cold or allergic reaction. Only a medical professional can diagnose the true source of these symptoms.

Solutions for Improving Indoor air

While providing us cooling and heating our air conditioning units can be made to be healthier. Fortunately, we have many ways in which to diminish poor indoor air quality and actually improve the air we breathe. The first way to improve indoor air is with a Dedicated Outdoor Air System (DOAS) to continually bring in fresh air and circulate it in spaces.

Fortunately, we have many ways in which to diminish poor indoor air quality and actually improve the air we breathe. The first way to improve indoor air is with a Dedicated Outdoor Air System (DOAS) to continually bring in fresh air and circulate it in spaces. A DOAS system will remove humidity from the room and help the AC unit operate more efficiently. Additionally, filtration and air sanitization are helping to make buildings safer for occupants.

August 13, 2020 by Kevin Stepp

Understanding DOAS and comfort cooling differences

While indoor air quality and ventilation have been major focuses of the HVAC industry for a long time, many misconceptions remain about what these applications require in terms of equipment and design. Today’s post will parse some of the most common questions about DOAS and comfort cooling equipment.

Purpose of DOAS

A dedicated outside air system (DOAS) or energy recovery unit (ERU) conditions air from the outdoors and delivers it to a space. It is essentially a dehumidifier in that its primary purpose is to remove moisture from the air, so when that air enters the space it is not adding additional load. This contrasts with comfort cooling equipment whose purpose is to maintain a consistent temperature in the space.

How

In order to achieve a cooling effect, a comfort cooling device must provide air to the space at a temperature much lower than the set point for that space. A DOAS or ERU, for its part, is not concerned with the temperature in the space. It monitors the temperature and humidity of the outdoor air and gauges how much capacity it needs to remove the moisture. The DOAS/ERU then discharges dry, room neutral air (roughly 70°-72°F and 30-40% RH).

When you need comfort cooling

A comfort cooling device operates only when the temperature in a space rises above set point. An outdoor air system, however, will typically operate during all occupied hours. ASHRAE 62.1 requires outdoor air be brought into in buildings at all times, so these machines rarely rest.

What is a DOAS unit?

Outdoor air equipment typically discharges air off of its cooling coil at 50-55°. The low leaving air temp effectively strips moisture from the air. However, constantly delivering low temperature air to a space will over cool it, so a modulating hot gas reheat coil is added to reheat the leaving air to a room neutral temperature around 70°.

DOAS and ERU equipment often feature some form of capacity control. Because outside air in cooling seasons can range from 65° to over 100°, these machines must be able to vary the amount of dehumidification they provide. Staged compressors, variable speed compressors, and modulating hot gas bypass are all options.

Space Temperature Control?

No, an outdoor air unit cannot replace a traditional air conditioner as the only device responsible for maintaining temperature in a space. The outside air unit operates constantly, meaning it cannot be turned off when the space is satisfied. Constant operation in a space temperature control design would lead to unacceptable temperature swings. More importantly, the mode of operation for a DOAS/ERU is determined by outside air temperature and humidity, not by space temperature. Space temperature control would become problematic when the space calls for heating, but it is 65° and raining outside. The unit must ignore the space and dehumidify instead, or the space humidity will rise out of control.

Not One or the Other

In order to properly apply a DOAS or ERU, it must be teamed with a comfort cooling device. This decoupling strategy allows designer to meet ventilation requirements while properly controlling space temperature and humidity. Thankfully, at United CoolAir we have solutions for both. Inquire today for more information on our comfort cooling equipment, DOAS, and ERUs.

June 29, 2020 by Kevin Stepp

What is DOAS?

With Independence Day weekend approaching Americans are making plans to celebrate with cookouts, swimming, and other outdoors activities. These simple pleasures become even sweeter knowing that, when outside, we are breathing clean, fresh air. What some don’t know is that when we return to work, we are often returning to buildings that have been consciously designed to bring in fresh outdoor air. This fresh air creates cleaner and safer indoor environments. You don’t need to be in the backyard in order to breathe fresh air!

We refer to HVAC equipment specifically designed to condition outside air as DOAS equipment, or a Dedicated Outdoor Air System. The goal is to flush recirculated air from a building and replace it with clean air from outdoors. Doing so reduces the quantity of unwanted particles in the air by diluting their concentration.

How does a DOAS unit work?

While technologies and applications differ, most DOAS equipment operates on the same basic principles. Outside air, which in the summer is hotter and more humid than indoor air, must be cooled and dehumidified before being discharged into the space. If it were not, temperature and humidity in the building would skyrocket. Air passes across a cooling coil that reduces its temperature to around 50°-55°F. This process removes much of the moisture from the air. Because 50°-55° is too low to comfortably blow into a room, DOAS units often offer hot gas reheat as an option to heat the now-dry air up to a more comfortable 68-72°. Now, fresh air is ready to enter the space.

While we will likely return to work still thinking about the fun we had outdoors over the holiday, we can do so knowing that some of the outdoors is still with us.

To learn more about United CoolAir’s DOAS offerings, click the following link to our Omega Air product or call us to discuss how we can modify our other products to fit your DOAS application.

August 31, 2018 by Matt Hanson

Dedicated Outside Air Systems (DOAS) part 2

Adapting DOAS To Your HVAC System

There is a proven method that will meet the challenges of complying with the ASHRAE Standards. This method delivers precise amounts of ventilation to spaces regardless of load size, and do it cost-effectively. Known specifically as Dedicated Outside Air Systems, or (DOAS), the conditioned outdoor air separates from the air that controls the building’s space temperature (dry bulb). By having separate systems providing dehumidified and ventilation air and another for dry bulb temperature, there is an improvement of both humidity and space temperature control. By conditioning the outdoor air and recirculated air independently, Dedicated Outside Air Units effectively separates the sensible and latent loads.

The DOAS unit removes the latent load to control humidity, while the main HVAC unit removes the sensible load. The result is a comfortable temperature for the space occupants. This is important because the primary source of building humidity in most climate areas is fresh outdoor ventilation air is improper dehumidification. Additionally, the DOAS unit can assist the main HVAC unit by controlling smaller internally generated amounts of latent load. This latent load naturally builds from occupants and other sources. It does this by providing air that is slightly drier than the target humidity level. Generally speaking, a Dedicated outside air unit provides a “neutral” air of 70ºF to 72ºF @ 50% RH.

What About Dehumidification

A DOAS unit can also provide the dehumidified air directly to spaces at 55°F where it will offset some of the sensible load of the local HVAC unit. By delivering the air “cold”, this operation strategy doesn’t waste the sensible cooling byproduct performed by dehumidification. This results in the local heating/cooling units sized smaller and require less valuable floor space. A smaller main heating/cooling system means less energy consumption through smaller fans and compressors. A DOAS delivering cold supply air requires less reheat, but some reheat could happen during periods of low sensible loads. In this way, there is not “over-cooling” by the DOAS unit.

A DOAS doesn’t rely on new technology but rather uses HVAC equipment configured to condition outdoor ventilation air separately from return air. The outside air conditioning system design consists of a cooling/dehumidification-reheat coil and a supplemental heating system. The deep evaporator coils consist of 10 fins per inch/6 rows deep design, positioned in the draw- through airflow arrangement. It is this technique that differentiates it from conventional HVAC systems. This configuration will cool and dehumidify air in the summer and heat or cool it in the winter. The design with outdoor air first passing through an optional preheat coil (if used), is sometimes used for winter operation. By using a heat exchanger, bringing the outdoor air closer to the temperature and humidity of the conditioned exhaust air is achieved.

Dedicated outside air units provide design engineers with installation flexibility to meet the requirements of the application. Variables facing the engineer include; new construction, retrofit, or installations having an existing system in place. Other considerations include the type of new or existing HVAC system installed such as constant volume, VAV, and even the newer variable refrigeration flow (VRF) terminal units.

All About Ducting a DOAS

Delivering the conditioned OA from the DOAS to where it’s needed usually includes a separate ducting system. This system runs parallel to the HVAC supply air. For many climates, an independent duct system is the best choice because the ventilation air volume better meets the volume requirements of the project. Furthermore, the DOAS ducting can be smaller than the conventional HVAC saving on the installation cost. Smaller ducting is also easier to manage in retrofit and existing HVAC installations.

A popular alternative ducting choice is a single duct system where the conditioned OA is blended with return air from the main HVAC system. For this, we use a mixing box, or in a terminal unit that serves just one zone. If using a multi-zoned HVAC control system, individual zones are controllable separately. In this way, the DOAS will deliver the proper amount of outdoor air directly to each zone. In all cases, the DOAS can vary the fraction of ventilation to supply air, which can reduce the outdoor airflow rate by 40 percent. This is due to only conditioning the amount of air necessary for each zone.