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 wall-mounted, indoor units ideal for hotels, apartment complexes, and other commercial or residential buildings. 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 the 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.
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.
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.
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.
Definitions
Air Filter Inspection
Air Filter Inspection involves visually examining air filters to determine if they require replacement to ensure optimal HVAC system performance and indoor air quality. A technician inspects the filter for dirt, debris, damage, and overall efficiency in capturing airborne particles while assessing the cleanliness of the filter material and the integrity of the frame. This may involve evaluating the filter’s MERV (Minimum Efficiency Reporting Value) rating for compliance with the HVAC system’s requirements, checking the airflow to ensure it’s unobstructed, and measuring the pressure drop across the filters to determine if they are excessively clogged.
Air Handlers (AHUs)
Air handling units (AHUs) draw in air from rooms through return ducts, pass it through cooling coils to reduce temperature and dehumidify or heating coils to increase temperature and regulate humidity, and then distribute the conditioned air back into the rooms through supply ducts. AHUs also feature filters that effectively remove dust, pollen, and other particles from the air, improving indoor air quality. These units are typically installed inside a building, usually in a mechanical room or basement.
Indoor unit
The indoor unit consists of an evaporator and blower housed in a large sheet metal enclosure. At the top plenum, the evaporator coil, or “cold coil,” absorbs heat from the warm air passing over it, enabling effective cooling and dehumidification. At the bottom of the enclosure, a furnace generates heat by burning fuel (such as gas or oil) or using electricity, working in tandem with a blower that distributes the heated air evenly throughout the space via ductwork.
Outdoor unit
The outdoor unit consists of a compressor, condenser, “warm coil” condenser coil, and fan. In heating mode, the condenser acts as a heat pump, which can provide both heating and cooling functions. Alternatively, a furnace can be used for heating purposes.
Mechanical Piping Clearance
Verify that mechanical and fire protection piping maintains sufficient clearance from electrical equipment, such as evaporator and automation control boxes, to ensure compliance with code requirements and prevent potential hazards. Install protective PVC ducts or housings, known as wire ducts or wire channels, for black (hot) wires to pass through, minimizing the risk of damage and electrical issues.
Preventive Maintenance (PM)
Perform preventive maintenance (PM) regularly, ideally at least once a year, to maintain coil cleanliness and efficiency, as well as overall HVAC system performance. PM includes inspecting and cleaning coils, checking and replacing air filters, lubricating moving parts, and inspecting electrical connections. By removing debris or buildup, coils can effectively absorb heat from indoor air during the cooling process, ensuring optimal HVAC performance when air is circulated back into the living space.
Rooftop Units (RTUs)
Rooftop units (RTUs) are self-contained units installed on the roof of a building. They house all essential components, such as the compressor, condenser coils, evaporator coils, fans, and controls, within a single enclosure. RTUs draw in fresh air from outside, condition it through cooling or heating processes, and distribute the conditioned air directly into the building’s interior.
HVAC Zone
An HVAC zone is a specific area within a building served by its own dedicated system. For optimal temperature control in a two-story home, consider using two separate AC units—one for each level. This approach ensures consistent temperatures and maximum comfort throughout the house. Since the second level typically experiences higher temperatures than the first, having a dedicated AC unit for each floor guarantees efficient cooling across the entire home.