Rooftop Packaged Units
Rooftop package units or RTUs are created with portability in mind. Thus, every unit is factory charged and are self-contained systems. As a result, there is no need to bring in an installation crew to install the customary refrigerant lines and perform perfunctory checks on the unit. Also, users have the option of configuring the RTU as a single circuit or multiple circuits. It is important to take note that in a multiple circuit set-up, the unit utilizes at least two refrigerant circuits. In most cases, the said packaged units are usually installed in a building’s rooftop. Thus, the acronym RTU was coined to signify a rooftop unit. In a typical building, several RTUs are installed to satisfy the structure’s cooling requirements. Thus, it is important to label the RTUs, creating an efficient way to track and monitor each corresponding thermostats. This monitoring scheme is employed so that technicians are not going to have a hard time linking a thermostat to its mother RTU.
Installation of RTUs
In a typical scenario, technicians install RTUs directly above the space that requires cooling or heating services. However, some locations do not allow a conventional set-up process. Locations are selected based on certain standards that prevent the entry of contaminants and ensuring a high level of air quality flowing through the ventilation system. Aside from considering the position of the RTU about walls and the building’s interior corners, it is also imperative to follow clearance guidance and the prerequisites dictated by information in the RTU’s installation and service data. It is also important to consider the technician’s ease of access to the said RTU. Technicians must have easy access to all aspects of the RTU to deal with repair and maintenance concerns.
Economizers
RTUs are usually equipped with economizers. An economizer is a mechanism that enables RTUs to reduce cooling costs by allowing cooler outside air rather than forcing the compressor to do all the cooling work. Economizers possess the capability of measuring the dry-bulb temperature and the actual heat content or the enthalpy of the outside air. In other words, the sensors are not only able to measure the heat content of the two airstreams, these sensors are also able to compute the difference between the outside air and the air inside the building’s occupied space. The process of allowing the cooler outside air into the building is called free-cooling.
Dual Enthalpy Sensor
An RTUs enthalpy sensor is comprised of a solid-state temperature and humidity sensors. The dual sensors work in tandem to regulate the flow of outside air into the building. The best type is the dual enthalpy sensors that measure the heat content of the outside airstream as well as the airstream within the building. If a system is limited only to the use of a sensor that measures the outside air, the free-cooling phase is initiated once the enthalpy of the outside air drops down to a predetermined set point. The said value is based on the cooling requirements of the building or workplace.
Ashrae Standard 62
The Ashrae Standard 62 is the gold standard when it comes to the acceptable air temperature of indoor workplaces. The said standard was updated in 2001, but it was in use since the year 1973. The local government implements building codes utilizing values dictated by the Ashrae Standard 62, specifically the ventilation levels in offices, factories, and residential structures. Aside from determining the optimum air temperature inside commercial and residential buildings, the Ashrae framework also provides guidelines when it comes to air cleanliness, air filtration, humidity, the elimination of contamination sources, and other elements related to indoor air quality. A crucial feature of the said compliance standard compels designers and building administrators to study the possible entry point of contaminants. For example, exhaust vents, exhaust fumes from vehicles, garbage dumpsters are some of the common sources of contaminants. The said framework makes it easier to figure out if the cooling systems can filter the entry of outside air. Also, Ashrae Standard 62 provides the values that help determine the predetermined setpoints when it comes to the use of economizers.
Demand Control Ventilation
The economizer provides a rigorous validation system that prevents the unwanted entry of outside air, as long as the temperature and volume do not correspond to predetermined settings. It is important to point out that the predetermined setpoints were established based on the expected number of people that are going to use the occupied space of a shopping a store or an industrial structure. Thus, the system does not discriminate between the actual and expected number of occupants. As a result, the compressor or the free-cooling mechanism of the economizers are always at work even if the temperature inside the building is already dropping at a fast rate due to the smaller number of occupants inside the buildings. The solution to this problem is the integration of the “demand control ventilation” strategy or the DCV. The DCV mechanism enables building administrators to adjust the entry of outside air based on the actual number of occupants.