An HVAC system is described having components of a variable refrigerant flow (VRF) outdoor compressor unit connected to an indoor fan coil unit. The indoor fan coil unit supplies air to ducts that condition a plurality of zones. Each zone has a volume modulating air damper that can maintain a predetermined volume of air flowing through it. As the dampers for some zones vary between open and close positions, the air pressure in the ducts changes. The volume modulating dampers compensate for these pressure changes, ensuring that only the predetermine volume of air is passing into the zones. By regulating the volume of into each zone, the volume modulating air dampers can restrict the air volume through the fan coil causing the outdoor unit to reduce compressor speed, thereby saving energy.

An in-line device for controlling a ventilation system for an enclosed space is featured. The ventilation system is configured to produce a first airflow from an external environment to the enclosed space and a second airflow from the enclosed space to the external environment. The in-line device includes a first electrical interface configured to connect to an electrical outlet, a second electrical interface configured to receive a power plug for the ventilation system, and a controller configured to control the ventilation system based on a first parameter of the first airflow and a second parameter of the second airflow.

Control systems are provided that provide thermodynamically decoupled control of temperature and relative humidity and/or reduce or prevent frost formation or remove previously-formed frost. The control systems herein may be included as a component of a heating, ventilation, air conditioning, and refrigeration system that includes a heat exchanger.

The invention relates to method (600) for operating an HVAC system, the method comprising: obtaining (602) a plurality of directly measured parameters from one or more data sources; determining (604) one or more indirectly measured parameter based on one or more of the plurality of directly measured parameters; and monitoring (606) energy flow of the HVAC system, based on the plurality of directly measured parameters and the one or more indirectly measured parameters, wherein the energy flow corresponds to heat transfer between the heat transfer medium and the air. The invention further relates to a an apparatus for operating an HVAC system which comprises means of monitoring an energy flow, based on a plurality of directly measured parameters and one or more indirectly measured parameters.

A method for calibrating a flow sensor in a heating, ventilation, or air conditioning (HVAC) system. The method includes receiving, at a controller, a request to enter a calibration mode and, in response to receiving the request, automatically commanding a flow control device to achieve a target flow rate. The method further includes generating, by the controller, calibration data for the flow sensor using a reference flow value of the flow rate when the flow control device has achieved the target flow rate and a corresponding flow measurement from the flow sensor.

The invention relates to a method for controlling a passive-ventilation system of a building, comprising: determining an outdoor air temperature of air in an environment of the building; determining an indoor air temperature of at least one zone inside the building; calculating a temperature difference by subtracting the determined outside air temperature from the determined indoor air temperature; and, if the calculated temperature difference is greater than zero, controlling a state of at least one passive-ventilation device of the passive-ventilation system to be in any of a closed state, an open state, and one of one or more intermediate states between closed and open state. Each of the states corresponds to one value of an opening fraction value of the at least one zone inside the building varying between 0 and 1.

Methods, systems, and devices for humidifying are described herein. One method includes determining a temperature in a space associated with a humidifying unit, determining a relative humidity in the space, determining an air speed associated with the humidifying unit, and adjusting an amount of water sprayed by the humidifying unit based, at least in part, on the temperature, the relative humidity, and the air speed.

A temperature control system. The control system includes a flow sensor configured to monitor water flow through a valve, an actuator coupled to the valve, and a first controller configured to establish a setpoint for a second controller. The second controller monitors fluid flow through the valve and combines a weighted first command from the first controller and a weighted second command from the second controller to generate a control signal, wherein combining the weighted first command and the weighted second command is based on the reliability of the flow sensor. The second controller further controls the actuator based on the control signal.

An HVAC system is described having components of a variable refrigerant flow (VRF) outdoor compressor unit connected to an indoor fan coil unit. The indoor fan coil unit supplies air to ducts that condition a plurality of zones. Each zone has a volume modulating air damper that can maintain a predetermined volume of air flowing through it. As the dampers for some zones vary between open and close positions, the air pressure in the ducts changes. The volume modulating dampers compensate for these pressure changes, ensuring that only the predetermine volume of air is passing into the zones. By regulating the volume of into each zone, the volume modulating air dampers can restrict the air volume through the fan coil causing the outdoor unit to reduce compressor speed, thereby saving energy.

A problem to be solved by the present disclosure is to realize a fan unit capable of determining occurrence or non-occurrence of a backflow during operation. In a second unit, a second controller calculates front-rear differential pressure by substituting a rotation speed and a volume of air or a wind speed that can be acquired in real time into a relational expression. The relational expression derives, from two values of the rotation speed, the volume of air or the wind speed, and the front-rear differential pressure, the remaining one value. Then, the second controller determines that a backflow occurs if the calculated front-rear differential pressure is within a range that cannot occur under a normal condition. Therefore, the occurrence of a backflow can be detected without using an expensive pressure sensor or a directional wind speed sensor.