Mechanical Design

Central Systems

Central systems efficiently deliver heating and cooling to multiple zones within a building. Typically found in larger buildings like offices, schools, and hospitals, these systems consist of a furnace or boiler for heating, an air conditioner or heat pump for cooling, and a network of ductwork for air distribution. While all split systems are a type of central air, not all central air systems are split systems—packaged HVAC systems, where the components are combined into a single unit, are another common configuration. 

Mini-Split Systems

Mini-split systems consist of one or more indoor units and an outdoor unit connected by refrigerant lines. Mini-split systems are ductless, while split systems use ductwork. Both systems operate on a direct expansion refrigeration cycle to provide efficient heating and cooling. The indoor unit houses the evaporator coil and blower, while the outdoor unit contains the condenser coil and compressor.

Packaged Terminal Air Conditioner (PTAC)

PTAC systems are installed through an exterior wall using a wall sleeve, with the outdoor section extending beyond the building facade. These self-contained units are commonly used in hotels, apartment complexes, and other commercial or residential buildings for efficient, localized climate control. These systems primarily provide cooling and are commonly used for individual room applications. During colder months, PTAC units require external heating sources, as they don’t have built-in heating capability. Some PTAC units seamlessly integrate with the building’s hot water system, using circulating hot water from a boiler to generate heat, ensuring efficient heating. They also feature a separate coolant chamber to deliver cool air when needed.

Packaged Terminal Heat Pump (PTHP) Systems

PTHP systems use refrigerant to transfer heat, providing both heating and cooling. These air-source heat pumps extract heat from the outside air, even in cold temperatures, and transfer it inside during heating mode. This makes them highly energy-efficient and versatile, as they can be used year-round without the need for an additional heating system. Commonly found in hotels, apartment complexes, and other commercial or residential buildings, PTHP systems are valued for their compact size, ease of installation, and flexible temperature control.

Window-Mounted Systems

Window-mounted systems are affordable and easy to install in a partially open window without requiring professional design or installation services. However, they occupy window and floor space, may vent warm air back into the room, and can generate noise.

Geothermal Heat Pump Systems

Geothermal heat pump systems, also known as ground-source heat pump (GSHP) systems, harness the earth’s stable temperature to provide energy-efficient heating and cooling. These systems extract heat from the ground through a network of pipes buried in the earth, taking advantage of the relatively constant underground temperature year-round. While the initial installation costs may be higher due to the need for ground-loop systems, geothermal heat pumps offer significant long-term energy savings and environmental benefits.

It’s important to note that air-sourced and water-sourced heat pumps also exist but are not considered geothermal systems, as they rely on ambient air or water sources for heat transfer rather than the earth’s temperature. Compared to traditional electric resistance heating systems, like furnaces and baseboard heaters, geothermal heat pumps are more efficient because they move heat rather than generate it, resulting in lower electricity usage for the same amount of heating or cooling. 

Combined Heat & Power (CHP) Systems

Combined Heat and Power (CHP), or cogeneration, is a system that simultaneously produces electricity and thermal energy from a single fuel source. Unlike conventional power generation, where excess heat is typically wasted, CHP captures and utilizes this heat for heating, cooling, or industrial processes. This approach improves overall energy efficiency, reduces fuel consumption, and lowers emissions. CHP systems are commonly used in commercial, industrial, and institutional settings where there is a continuous demand for both electricity and thermal energy.

Chilled Beam Systems

Chilled beam systems provide energy-efficient cooling and heating by using water to absorb and remove heat from a space. Unlike traditional air-based HVAC systems, chilled beams rely on convection and radiant cooling, reducing the need for large ductwork and improving thermal comfort. Active chilled beams, in particular, offer several advantages: they use significantly less supply air compared to conventional systems, minimizing the fan energy required to circulate air. By using water as the primary cooling medium—due to its higher heat capacity—chilled beams transfer more heat with less air movement, resulting in greater efficiency. Additionally, they can be zoned to provide cooling only where needed, further reducing unnecessary energy usage.

Active Chilled Beams

Active chilled beams integrate with a building's ventilation system, using a ducted air supply to enhance both cooling or heating while offering better control over temperature and humidity compared to passive chilled beam, which relies on natural convection. A primary air system delivers conditioned air through nozzles, creating an induction effect that draws room air through a water-cooled coil.

Passive Chilled Beams

Passive chilled beams operate without mechanical air supply. Warm air rises, passes over a chilled water coil, cools, and then descends, creating a continuous cooling cycle. These systems are highly efficient for radiant cooling and perform best in dry climates or low-humidity spaces, as they don’t actively remove moisture through supply air. They are typically used in conjunction with a separate ventilation system.

Hybrid and Dual-Fuel Systems

Hybrid and dual-fuel systems combine a gas furnace with an electric heat pump, offering flexibility and energy savings. They use the heat pump for heating when temperatures are mild and switch to the gas furnace when temperatures drop significantly.

Variable Refrigerant Flow (VRF) Systems

Variable Refrigerant Flow (VRF) systems utilize refrigerant to deliver highly efficient heating and cooling. These systems offer simultaneous heating and cooling capabilities in multiple zones, ensuring precise temperature control. VRF systems achieve energy savings through modulating refrigerant capacity, eliminating the need for constant cycling seen in traditional HVAC systems. Additionally, VRF systems optimize energy use by redistributing excess heat from cooled zones to areas requiring heating, maximizing efficiency through heat recovery.

Direct Expansion (DX) Systems

Direct Expansion (DX) systems operate differently than chilled water systems by using refrigerant to absorb and release heat directly within air handling units or split systems. Each indoor unit contains its own compressor and refrigerant circuit, allowing the system to provide cooling at the point of use.

In a DX system, the refrigerant circulates between the indoor and outdoor units through a series of coils, undergoing phase changes to absorb and release heat in a vapor compression cycle. During this process, the refrigerant absorbs heat from the warm air passing over the evaporator coil, cooling the air before it is recirculated back into the space.

DX systems are often preferred in residential and light commercial applications for their simplicity and energy efficiency in smaller spaces or individual zones. Additionally, they can provide heating through a process called “heat pump” operation, where the refrigerant flow is reversed to extract heat from the outdoor air and release it indoors.

Chilled Water Systems

Chilled water systems operate differently than traditional air-based HVAC systems by utilizing chilled water to absorb heat from a building’s interior for cooling purposes. In this setup, a central chiller plant produces cold water, which is then circulated through a network of pipes to air handling units (AHUs) or fan coil units (FCUs) located throughout the building. As the chilled water passes through these units, it absorbs heat from the surrounding air, thus providing cooling to the occupied spaces.

One of the key advantages of chilled water systems is their ability to offer individual room temperature control, making them an excellent choice for large commercial buildings and spaces with varying cooling needs. Additionally, chilled water systems can be designed to provide heating by using a boiler to heat the water, allowing for efficient and comfortable temperature control in various climate conditions.

Energy Recovery Ventilator (ERV) Systems

Energy Recovery Ventilator (ERV) systems are designed to improve indoor air quality, reduce energy consumption, and enhance occupant comfort by recovering energy from exhaust air and using it to precondition the incoming outside (fresh) air. These systems are typically installed as part of a building’s HVAC system and consist of a heat exchanger, fans, and ductwork.

In an ERV system, stale air is exhausted from the building, passing through the heat exchanger, where heat and moisture are transferred to the incoming outside air. This process reduces the energy required to heat or cool the incoming air, as it is already partially conditioned by the recovered energy.

ERVs are particularly useful in applications with high ventilation requirements, such as schools, offices, and healthcare facilities, where maintaining good indoor air quality is essential. They are also suitable for use in various climate conditions, as they help to mitigate the impact of temperature and humidity extremes on the building’s HVAC system.