Kevin Stepp, Author at United CoolAir

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.

January 6, 2020 by Kevin Stepp

Recovering Energy from Class 2 Exhaust Air

The Problem

Providing a healthy environment must be the top priority for any air conditioning design. This can be difficult though, especially in spaces that generate less-than-ideal breathing conditions. Nail salons, health clubs, and bathrooms are just a few examples of spaces where processes or people taint the air with undesirable chemicals or odors. In these spaces, building designers are missing an opportunity to save valuable energy while providing healthy buildings.

ASHRAE 62.1 – 2019 designates air in these spaces as Class 2 air and stipulates that it must be exhausted. Fresh, but expensive to treat, outside air must be brought into the building to replace the exhaust. Here, designers are dropping the ball if they simply throw away the exhaust air. It contains valuable heat energy that should be recovered and used to reduce the energy needed to condition outside air.

The Solution

United CoolAir’s Alpha Aire utilizes two energy recovery devices to extract heat energy from the exhaust and pre-cool (in summer) and pre-heat (in winter) outside air before it reaches a coil. The unit design reduces the load on the cooling and heating coils to as little as 1/3rd that of a standard outside air unit. At a fraction of the operating cost, Alpha Aire delivers room-neutral (roughly 73° and 50% RH), fresh air to a building.

One common concern with Class 2 applications is whether the exhaust air will be transferred back into the building by way of the energy recovery wheel. United CoolAir utilizes a molecular sieve enthalpy wheel with a rated EATR of 0.5% or less. This means that less than one half of one percent of air leaving the building will be trapped in the wheel and recirculated into the space, a rate undetectable to humans and one far lower than the 10% allowed by ASHRAE 62.1 – 2019.
Designers should not hesitate to use all of the energy at their disposal. Alpha Aire gives them the opportunity to do just that. Call or click the link above to find out more.

Applications

Toilet rooms	Nail salons	Museums
Locker rooms	Pet shops	Hotels
Shower rooms	Barber shops	Health clubs
Science labs	Restaurants	Laundry rooms
Libraries	Bars	Pharmacies
Art classrooms	Bowling alleys	Churches