loadmodeling.tool Version 2.5: Air System Inputs & Defaults

In loadmodeling.tool Version 11.19, cove.tool unveiled the Air Systems functionality. The Air Systems functionality helps engineers reduce the time required to model and run complex Air Systems that are becoming more common in sustainably designed buildings. With the release of loadmodeling.tool Version 2.5, the platform now comes equipped with new Air System types to improve the product's accuracy and help engineers reduce the time required to model and run complex systems, which are becoming more common in sustainably designed buildings.


Air Handling Units (AHU) Sizing and Selection

Air Handling Units (AHUs), also known as Air Systems, come in various configurations and scopes, so selecting and right-sizing a system can pose a significant challenge for engineers. Air Systems include fan coils and blower coils, packaged systems, modular AHUs, and custom AHUs. Each system type serves a unique purpose, depending on various factors including the location of the building and the type of space it is used in. loadmodeling.tool is specifically designed to help mechanical engineers select and right-size air systems for optimal efficiency and mitigated environmental impact.


loadmodeling.tool Version 2.5 Air Systems Include:

  • Active Chilled Beams

  • Parallel Fan-Powered Boxes

  • Series Fan-Powered Boxes

  • Induction Units

  • Local Fan Coil Units

  • Packaged Terminal Air Conditioners (PTAC)

  • Water to Air Heat Pumps (WAHP)

  • Energy Recovery Ventilators (ERV)

  • Packaged Terminal Heat Pumps (PTHP)

  • Unit Heaters

  • Radiant Cooling Panels (RCP)

  • Baseboard Heaters

Active Chilled Beams

Unlike radiant panels and chilled sails, Active Chilled Beams (ACBs) actively cool a space through induction and force convection. ACBs have ductwork supplied to them, providing a specific amount of primary air to the pressurized plenum within the device. Primary air is discharged through induction nozzles and mixed with entrained air to ventilate the room. ACBs are sensible cooling only units, removing the need for drain pans and condensate collection systems. There are various advantages to using active chilled beams, including but not limited to:

  • Reductions in the initial cost of equipment

  • Increased occupant comfort

  • Increased energy efficiency 

  • Ease-of-operation and maintenance

Parallel Fan-Powered Boxes

Parallel Fan-Powered Boxes are engineered to provide high performance and ease of installation. Unlike traditional systems, the primary air and recirculated air sections operate independently, allowing both sections to be controlled by the same input. Additionally, Parallel Fan-Powered Boxes enables the primary airflow to supply the cooling demand, while recirculated air provides heating volume. This allows central air handling units to be shut down in unoccupied operation, while the recirculated air maintains minimum temperature in each space.

Series Fan-Powered Boxes

Series Fan-Powered Boxes, sometimes called Series Fan-Powered Terminal Unites act as boosters for the air handler, as their fans are used to move air the rest of the way to the zone. Their fans run continuously during occupied periods to provide constant air motion and sound levels.


Induction Units

Induction units are air terminal units that cool and disperse air through a duct system. Induction units enable air to spread through nozzles, matching air temperature with heat exchanges and pushing the air into rooms with the primary air through the outlet. The basic unit consists of a conditioned air supply air inlet, a damper/jet flow nozzle, an actuator, a velocity sensor, and a return air damper. The primary difference between an induction unit and an ACB is the induction unit can deliver latent cooling, however this then requires handling the condensation from the cooling coil.


Local Fan Coil Units (FCU)

Fan coils are commonly used in all types of buildings and are typically applied in a Dedicated Outdoor Air System (DOAS). In an FCU, there are two main ducts that are used – the supply duct and the return duct. The fan coil units are connected to either a heating or cooling coil, or both. When the system is activated, a motorized fan within the unit forces air into smaller, localized ducts that strategically distribute air within a room. 

High-performance FCUs are typically used to move greater air volumes when there is higher static pressure and to reduce noise levels. These FCUs use larger blowers to reduce outlet velocity and fully enclose the fan assembly in an insulated casing. High-performance FCUs also provide better temperature control.

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Packaged Terminal Air Conditioners (PTAC)

Packaged Terminal Air Conditioners (PTACs) are among the most common air conditioning solutions. They are self-sustained heating and cooling systems, typically used to heat or cool a living space using only electricity. However, some are cooling-only PTACs with external heating through a hydronic heating coil or electric resistance heating system. They are often found in buildings such as hotels or residential since they are easy to use and significantly reduce owners' energy costs. PTACs often come in the form of window air conditioners, and older units usually rely on mechanical controls. Most PTAC systems include the following controls:

  • Time Control

  • Mode Control

  • Temperature Setting

  • Energy Saving Mode (Sleep Mode)

Water to Air Heat Pumps (WAHP)

Water to Air Heat Pumps (WAHPs) are commonly used in residential and some office buildings and are comprised of both indoor and outdoor units. The components are connected via piping that transports water between the external and internal components. The outdoor units include some form of heat reject, such as a cooling tower, and a heat source, such as a boiler. The local heat pump units reject or take heat from the water loop to condition each space. Key benefits include:

  • Energy and system efficiency

  • Improved indoor environmental quality

  • Reduced mechanical footprint

  • Lower maintenance cost

  • Improved system hygiene

Energy Recovery Ventilators (ERV)

Energy Recovery Ventilators (ERV) are systems which draw clean, fresh air into a home or office to remove stale air. The heat exchanger facilitates the transference of heat and moisture in the exhaust air stream to the ventilation air stream. The ventilation systems capture pollutants and allergens from the outside air via filters to ensure high air quality within the building.

The ERV system pre-cools and dehumidifies during the warmer seasons and humidifies and pre-heats during the cooler seasons. ERV systems can help HVAC designers comply with ASHRAE standards by reducing total HVAC equipment capacity and system energy consumption. Other advantages include:

  • Ability to maintain 40-50% indoor relative humidity

  • Improves energy efficiency

  • Good building IAQ


Packaged Terminal Heat Pump (PTHP)

A Packaged Terminal Heat Pump (PTHP) is the heat pump version of a PTAC. PTHPs use refrigerant to remove or add air to an indoor space as needed and incorporate electrical backups for heating in winter temperatures. The same unit that was used for cooling is used for heating in the cooler seasons. The system utilizes a 4-way valve to reverse the flow of the refrigerant in a heating cycle known as reverse cycle.

Some units come with an auxiliary heater, which is used to supplement the heating process when the heating capacity is insufficient during the cooler months. PTHPs are high-efficiency appliances, designed to reduce the risk of refrigerant leaks with a high impact on climate change. 

Unit Heaters

A unit heater is a stand-alone appliance serving to heat a given space and capable of operating on different energy sources. Typically found in back of house spaces, energy sources can include, hot water, steam, fossil fuels, propane, or natural gas. 

Radiant Cooling Panels (RCP)

Radiant Cooling Panels (RCP) cool air using water circulated through tubing embedded in its surfaces. The panels allow surfaces to absorb long-wave thermal radiation given off by building occupants and appliances. Its imperative for RCPs to remain above the dewpoint temperature (at least 3 °F) of a space to prevent condensation from occurring. RCPs have several advantages, including:

  • Energy Efficiency

  • Superior Thermal Comfort

  • Architectural Flexibility

Baseboard Heaters

Baseboard heaters, sometimes called electric resistance heaters or fin tube, are a form of zone heaters that separately heat individual rooms of a house or other building. Unlike forced air systems, they don't push air, preventing dust and allergens from entering a space. Advantages of baseboard heaters include:

  • Low noise

  • Direct offset of envelope loads

  • Secondary heat source

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Why is this feature important?

An Air System defines how air is delivered to the spaces within a building. Including new Air System inputs and defaults allows engineers to add Air Systems to their models more quickly and with increased accuracy. With the powerful outputs provided for each system including the cooling, heating peak sizing and coincident peak airflows, engineers are able to work with manufacturers to select and then document these major pieces of equipment on each project. 


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