The refrigeration cycle of an HVAC system is governed by the principles of thermodynamics, or the transfer of energy from one place to another. The key concept is that heat is a form of energy corresponding to a definite amount of mechanical work. Key Concepts Boiling or evaporation means changing from a liquid state to a gas state. Heat of vaporization is the amount of heat that is required to convert a liquid into a gas (boiling point). 212 degrees Fahrenheit is the boiling point of water at sea level. Lower pressures (above sea level) make it easier for a liquid to boil, and higher pressures (below sea level) make it more difficult. There Is No Such Thing as Cold […]
Mechanical Systems
Chiller System Basics
Small air conditioning units are often suitable for general residential and light industrial applications, but once a building reaches a certain size, it becomes more efficient to use a centralized chilled water system. Chillers use a refrigerant gas to move the unwanted heat between the evaporator and the condenser. The chilled water is generated in evaporator and this is sent around the building by a pump to collect the unwanted heat and bring it back to the evaporator to be cooled down. The refrigerant collects this heat and moves it to the condenser. The condenser puts this unwanted heat into another loop which is sent by a pump to the cooling towers to send it into atmosphere or it will […]
Cooling Tower Basics
The purpose of a cooling tower is to reject the unwanted heat from the condenser water loop of a building or process. The condenser water leaves the condenser of the chiller at around 32°C (89.6°F) and the pump sends this up to the cooling tower. When the warm condenser water enters the Cooling Tower, it is sprayed into small droplets across the “fill packaging” this increases the surface area of the water and allows for greater heat loss. The system has been designed so that the condenser water leaving the cooling tower and re-entering the chiller condenser, must be around 27°C (80.6°F) in order to be able to pickup enough heat on it’s next cycle. Open (Wet) vs. Closed (Dry) […]
HVAC Basic Troubleshooting
Frost build-up on evaporator coils Lack of airflow, dirty filters, dirty coils. Low suction in the condenser Low refrigerant charge or leaks. Blocked expansion valve (moisture, dirt, etc). Reduction of flow in evaporator. Leak detection Ultraviolet dye. Soap bubbles. Electronic detectors. First check all fittings and coils. If leak cannot be found, system must be reclaimed and pressure tested. Signs of leaking Freon Warm air supply and low airflow. Increase in electricity bills. Bubbling or gurgling noises. Refrigerant poisoning. Low suction pressure Insufficient heat getting to the evaporator caused by low airflow (dirty filter, slipping belt, restricted ductwork). Check for proper superheat. Defective, plugged, or undersized metering device. superheat doesn’t change, and the subcooling increases. Check sight glass. Obstructions in […]
Basic Mechanical Systems
All buildings generate unwanted heat, whether it be from solar heat gain, or generated by the occupants and equipment on the inside. This heat needs to be removed in order to keep the environment at a suitable temperature for critical equipment and the occupants inside. The design cooling load (or heat gain) is the amount of heat energy to be removed from a space by the Heating, Ventilation, and Air Conditioning (HVAC) systems to maintain indoor design temperature when worst case outdoor design temperature is being experienced. Air conditioners are designed to cool the air, but air temperature is influenced by humidity, and that needs to be part of the evaluation when you are sizing an air-conditioning system. Water vapor […]