News - United CoolAir

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.

August 25, 2018 by Matt Hanson

Dedicated Outside Air Systems (DOAS) part 1

Outside Air The late sixties, early seventies ushered a new era into many facets of our lives. Rising oil costs along and supply uncertainty made it necessary to evaluate what we had taken for granted for years.
The October 1973 Arab oil embargo sent oil prices rocketing while shortening oil supplies. This urged building owners/operators to search for more reliable, less expensive ways to heat and cool large commercial spaces. The solution was to create a sealed building envelope limiting the amount of infiltration and ventilation air to the minimum.
National energy conservation measures called for a reduction of outside air to 5 CFM per building occupant from 10 CFM. Most experts believed this would be sufficient ventilation to ensure adequate health and comfort, but they were quickly proven wrong.

The reduction in expensive OA resulted in a large increase in occupant complaints traced to their time at their workplace. Symptoms included nose or throat irritation, headache, dry cough, itchy skin, and sensitivity to odors, nausea, and eye discomfort. Sick Building Syndrome (SBS), as it was later known, sickened 221 people and lead to the death of 34 others. This occurred at an American Legion convention in Philadelphia through contamination in their air conditioning system.

Many studies have since proven beyond a doubt and established links between indoor air quality and human illness. When you consider the economic impact through lost productivity, lawsuits and increased insurance costs; building owners, HVAC design engineers and operators all take this issue very seriously.

OA is the Answer

ASHRAE Standard 62.1 – 2013—Ventilation for Acceptable Indoor Air Quality for commercial buildings — quantifies the minimum ventilation rates and indoor air quality that will be acceptable to human occupants. 62.1 intends to minimize the potential for adverse health effects and has increased average ventilation rates from 5 CFM/person up to 20 CFM/person.
As a result, the effect of humidity levels by the introduction of greater amounts of outside air is attainable. Humidity control becomes particularly important in the eastern half of the United States where mean dew point temperatures are 60°F e.g., 78°F/54% relative humidity, and higher during the summer. These issues influence the need for an HVAC unit design capable of controlling ventilation, moisture levels, and temperature in the space.

To rectify the problem, traditional central station comfort cooling air conditioners must be “oversized” to handle peak latent load. ASHRAE ventilation standards, require traditional air conditioning systems to reach 20% 70% more outside air than designed to cool, heat and dehumidify. Also, the traditional central HVAC provides the proper amount of outside air for spaces with the greatest ventilation requirements. This causes over ventilating the rest of the building in the process and increasing the cost of conditioning that air.

August 2, 2018 by Matt Hanson

Mold Prevention and IAQ Improvement

IAQ is a major concern and can have a devastating impact on your life. However, not providing the proper ventilation and fresh air in an occupied space can make people sick. Additionally, this can also have a major financial impact. Hundreds of schools annually are experiencing mold in their classrooms as you can see in the article below (Mold Case Study). A state office building in Texas experienced just this situation. As a result, the cost to the state of Texas was over $15,000 dollars. This incident also sent staff home which has an impact on productivity as well as financial cost. Mold prevention has become a vital element in keeping buildings safe for occupants.

Mold Case Study

United CoolAir has an IAQ Product designed to provide fresh air to avoid mold growth. In fact, Alpha Aire is a packaged Dedicated Outside Air System, Air Source Heat Pump with both an Energy Recovery Wheel and Plate Heat Exchanger. Having two devices in one unit brings in the fresh air at very low dew points while exhausting the interior space air to the outside. Follow the link below for more information on mold prevention with this revolutionary product.

Alpha Aire Overview

Please feel free to contact United CoolAir at (717) 843-4311 if you have any questions.

April 13, 2018 by Matt Hanson

Combining DOAS and VRF as an HVAC Solution

For decades, using Variable-air-volume (VAV) systems with air terminal units developed extensively in commercial/institutional buildings in the United States. Unfortunately, the optimized design of a VAV system with terminal heat is difficult at best. Mostly because of limitations inherent in VAV and complications posed by design standards and regulations. One new approach involves the pairing of a dedicated outdoor-air system (DOAS) with a variable-refrigerant-flow (VRF) system. By separating the goal of achieving ventilation rates from that of maximizing thermal comfort, we avoid conflicting situations forcing compromises. What’s more, we can simplify the design process and find system efficiencies that go far beyond those commonly achieved with VAV systems with terminal heating.

In the simplest VAV system, mixing incoming outside air and return air in a central air-handling unit (AHU) and then pre-heated or pre-cooled occurs. For each zone, a terminal unit adjusts airflow based on cooling demand. When a zone requires heating, reducing supply-air flow to a minimum setting and heated, typically via a terminal-unit heating coil is the solution.

In its simplest form, a DOAS is an AHU dedicated to ventilation, not sized to provide cooling air. DOAS often are supply-only systems with relief to outdoors; however, they also can include exhaust heat recovery. Generally, sizing does not provide 100 percent air economization (cooling using outside air in lieu of mechanical cooling).

VRF systems use individual high-efficiency fan coils in interior spaces in combination with high-efficiency condensing units that serve multiple zones. The arrangement of VRF systems provides energy recovery, moving heat from zones requiring constant cooling to zones that sometimes require heating.

Meeting Industry Standards

ANSI/ASHRAE Standard 62.1, Ventilation for Acceptable Indoor Air Quality, provides minimum outdoor-air-flow requirements for design conditions. ANSI/ASHRAE/IES Standard 90.1, Energy Standard for Buildings Except for Low-Rise Residential Buildings. Meanwhile, this requires some systems operations so ventilation capacity modulates to match ventilation load (i.e., demand). Designing systems to meet both of these requirements is complex.

To help match capacity to load, ANSI/ASHRAE Standard 62.1 allows “dynamic reset,” but leaves the details to the designer. A common approach combines system-level outside-air-damper reset with zone-level demand-control-ventilation (DCV) strategies. For VAV-system energy efficiency maximization, the system-level intake/exhaust/relief-damper-reset sequence is set for space-temperature control. This aide in the coordination of building pressure with an air-economization-reset sequence. Such controls can are quite complex, particularly when considering pressurization between zones and interaction with exhaust systems requiring variable-volume control. Weather conditions also can have a major impact on building pressurization and space ventilation.

Other common control sequences for large VAV systems include occupied-hours control, optimal start/stop, fan-pressure reset. It can also include (“critical terminal unit” control), “ventilation optimization”1 (DCV), ventilation space-temperature setback, supply-air-temperature reset. Finally, included are dynamic space-pressure control, economizer, energy recovery, natural ventilation, and interfaces with building lighting controls, smoke detection, fire alarms, and even security systems. The interplay between these control schemes vastly complicates efforts to optimize building energy use.

Meeting Zone Requirements

Further complicating VAV-system design is the need to follow the ANSI/ASHRAE Standard 62.1 ventilation-rate procedure. This standard asks designers to use the multiple-space equation (MSE) to calculate the “critical” zone, the space driving the overall (system-level) outside-air fraction. Zone-level flow changing follows to meet zone-level requirements. Once the critical zone has been chosen, heating-turndown requirements push designers to over-ventilate some zones by increasing heating minimum settings. This typically changes the critical zone and reduces the overall outside-air fraction at the central-system level, substantially affecting AHU components.

To respond to changes in zone population, dynamic reset of VAV systems, they often apply combining zone-level DCV with system-level ventilation reset. Ventilation reset is a control scheme by which the MSE is solved dynamically to change the system outside-air setpoint. This application with airflow-measuring stations, along with electronics and software to control dampers based on relative airflow, happens at the central system.

Maximizing Energy Efficiency

Central-system design usually is based on the static-condition (design) critical zone. While in the real world, the zone population varies dynamically along with building HVAC load (internal and weather-related) over the course of a day. Maximizing energy efficiency under these conditions pushes the envelope in terms of building system design and building-operation hardware and software. Some commercial software packages can aid ventilation reset, calculating critical ventilation zone per ANSI/ASHRAE Standard 62.1. Calculating the minimum system outside air, however, usually requires the overriding of some terminal-unit turndowns, which changes the critical zone.

This is allowed by ANSI/ASHRAE/IES Standard 90.1 because only a few zone overrides can change a system outside-air setting by many percentage points. This saves considerable pre-treatment energy and reducing central-system size. Meanwhile, inputs to these calculations vary with system load, which also can change the critical zone. At the same time, other overrides, such as of supply airflow for makeup to areas with exhaust flows exceeding ASHRAE minimum rates, are necessary. These overrides and simultaneous variations result in the need for iterative calculations involving all environmental variables; such calculations currently are beyond the scope of commercially available software.

Zoning is another limitation as history shows, building-construction economics can drive VAV-system designers to combine up to several rooms on a single ventilation and temperature-control zone. Because heating and cooling loads can vary widely between rooms in a single zone. This often leads to discomfort in certain rooms when other rooms in the same zone are not at the design load.

To Sum it Up DOAS and VRF

In summary, designing a VAV multi-zone HVAC system can be challenging to for DOAS and VRF, to say the least. Overlaying the various requirements, exceptions, and system functions results in iterative design simulations that must be re-run whenever a room’s size changes. Complying with all codes while addressing the competing interests of ventilation and energy optimization is theoretically possible. However, technical solutions partly exist and are being developed. In practice, designing and redesigning systems with complex, iterative calculations is not very practical, and manual overrides generally do not fully optimize system designs. Meanwhile, designers often estimate “block” (net) load based on building-envelope heating and cooling. Considering neither variations in internal and ventilation heating/cooling loads nor airflows needed for ventilation and space pressure control, significantly. The result is undersized or oversizing systems.

Fortunately, a design paradigm is emerging to compete with the old VAV model. This new model can reward us with simplified system design while letting us achieve the increased system efficiencies that energy costs are demanding

April 10, 2018 by Matt Hanson

Grow Room HVAC Units

The rapid increase of the cannabis industry within the United States creates a critical need for proper HVAC equipment in Grow Room facilities. Growing cannabis can be very tricky due to the fact it is grown indoors instead of outdoors like other crops. It is critical that cooling and dehumidification are the focus of their HVAC needs.
There are six main challenges that one will face when determining an HVAC system for a grow facility. Those six challenges are temperature, humidity, lighting, airflow, ventilation, and smart technology.

Grow room facilities typically need to be between 70°F-75°F with humidity between 50-60%. HVAC systems should be able to maintain the specific temperature to ensure growth for the plants. Also needed is the ability to quickly remove any additional humidity that may arise during the watering process. The lights used in these facilities also produce a large amount of heat, therefore, needing a strong HVAC unit to keep the rooms cool and prevent overheating.

Airflow is critical and your HVAC system should provide enough to create a “natural like breeze” to ensure the plants have constant movement and vibration. Equally important is the need to provide extensive filtration to the system. This will ensure smells cannot leak to the outside and prevents mold spore formation by capturing all dust and sediment. Lastly, your grow room cooling unit must have smart technology enabled in order to control all of the above mentioned or alert you if something goes wrong.

When it comes to selecting your HVAC unit for a grow room facility, you need to think of United CoolAir. United CoolAir can manufacture exactly what you are looking for in order to create a successful grow room. We have both the expertise and experience to provide you the best operational equipment in the USA.

March 20, 2018 by Matt Hanson

Dedicated Outside Air Systems (DOAS)

The late sixties, early seventies ushered a new era into many facets of our lives. The rising cost of oil and uncertainty of supply made it necessary to evaluate what we had taken for granted for many years. The October of 1973 Arab oil embargo sent oil prices rocketing while shortening oil supplies. This caused building owners/operators to search for more reliable, less expensive ways to heat and cool large commercial spaces. The solution it seemed was to create a sealed building envelope thereby limiting the amount of infiltration and ventilation air to the minimum.

National energy conservation measures called for a reduction of outside air to 5 CFM per building occupant from 10 CFM. Most experts incorrectly believed this would be sufficient ventilation to ensure adequate health and comfort. The reduction in expensive OA resulted in a large increase in occupant complaints traced to their time at their workplace. Symptoms included nose or throat irritation, headache, dry cough, itchy skin, sensitivity to odors, nausea, and eye discomfort. Sick Building Syndrome (SBS), as it became known sickened 221 people and killed 34 others at an American Legion convention in Philadelphia. Later discoveries concluded the contamination occurred through their air conditioning system.

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