Buildings are cooled using different types of HVAC systems and equipment, from ceiling fans to district chilled water (CHW) plants. While residential buildings and smaller commercial buildings are often cooled using air-cooled equipment, CHW systems are typically the engineer's preferred choice for larger buildings. A building containing a central plant with chillers, pumps, and appropriate ancillaries will provide a system that has the capabilities to accurately control supply air temperature at any entering air condition. This can be critical when designing systems requiring 100% ventilation air, or providing dehumidification in humid climates. This article will discuss a few things to consider when designing CHW systems. There are a number of different energy codes and standards that are adopted by jurisdictions throughout the world. While they have small differences, their intent is to ensure systems are designed to maximize efficiency. For this article, both ASHRAE Standard 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings and the International Energy Conservation Code (IECC) are discussed.

While the International Mechanical Code (IMC) lists a general requirement for CHW piping insulation, it refers to the IECC for specifics. Section C403.2.8 of the 2012 IECC states that all piping systems comply with Table C403.2.8. ASHRAE 90.1-2010 requires insulation thicknesses identical to the values listed in the 2012 IECC, using the baseline thermal conductivity. Building CHW systems are required to have some form of water-side economizer per current codes and design standards. Typically, this is accomplished using a plate and frame heat exchanger piped to the CHW and condenser water systems, although indirect evaporative cooling coils are also permitted. Section C403.4 of the IECC requires a water side economizer system to be incorporated into all CHW systems greater than 300,000 Btu/h output capacity. The economizer shall be capable of satisfying 100% of the expected cooling load at outdoor air temperatures of 50 F dry bulb/45 F wet bulb, with an exception for systems requiring lower CHW temperatures for dehumidification.

ASHRAE 90.1-2010 lists requirements similar to this, although it includes exceptions that allow computer rooms to activate the economizer at 35 F dry bulb instead of 50 F. It is important to understand that systems with an air side economizer will meet the economizer requirement, and water side economizers need only be sized for HVAC equipment still requiring CHW to meet cooling loads at the listed temperatures. Because the purpose of the economizer mode is to save energy, requirements are listed in the codes to ensure they are designed with this in mind. IECC Section 403.4.1.2 limits the pressure drop across the heat exchanger, or precooling coils, used for the water side economizer. It states that if the pressure drop across the heat exchanger is 15 ft or higher, then a secondary loop and circulating pump shall be provided so that the pressure drop through the heat exchangers is not seen by the CHW system during normal (non-economizer) conditions. One method to meet this requirement is to install motorized control valves at the heat exchanger connection, and connect the heat exchanger to the CHW system as another chiller in parallel.

This meets the requirement because water will only flow through the heat exchanger when economizer mode is enabled. A secondary pump would not be needed since the building's CHW and condenser water pumps could be used to flow water through the heat exchanger, provided they are equipped with variable frequency drives and can be adjusted to match the winter cooling load requirement. Most designers have no issues with incorporating the required components of a water side economizer into their designs; ac recovery recharge machinehowever, the most challenging part is how to control it. noise from air conditioning units victoriaBoth ASHRAE 90.1-2010 and IECC require water side economizer mode to operate at 50 F dry bulb/45 F web bulb, with possible exceptions if the building contains a computer room.12000 btu window air conditioner heater

The design complexities exist during times when outdoor air temperatures are at the higher end of economizer mode, or approximately 40 to 45 F wetbulb. The reason for the issue is most air handling systems are designed for the default CHW supply temperature, whether it is 42 F, 45 F, or somewhere in between. However, the CHW temperature during economizer mode may not be capable of delivering this water temperature, even with the most efficient plate and frame heat exchanger. Figure 1 shows offices around the perimeter, with additional offices, an electrical room, and an information technology (IT) room interior to the building. Assuming all of these spaces are conditioned using CHW/hot water fan coil units, served from a central plant delivering CHW at 42 F, the designer would select coils based on a CHW temperature of 42 F supply/58 F return. During the summer months,there shouldn't be any issues, as the fan coil units are properly sized to handle the peak cooling load with 42 F CHW and everyone is happy.

Vertical 500 to 1,500 Cfm Horizontal 750 to 2,000 Cfm Airstream unit ventilators meet the strict indoor air quality requirements of schools, hospitals, and institutions. The 40UV units are compact, efficient, and easy to install and maintain. Units are designed to provide economic, dependable long-term performance. Air conditioning is the treatment of air within a localized environment, this treatment may be heating, cooling, humidifying, dehumidifying, cleaning etc. the objective of this treatment is generally to make ourselves more comfortable where we work, live or play. The comfort of the human body generally depends on three factors: the temperature of the air, its relative humidity and the motion of the air. The temperature of the air is perhaps the most important factor to consider, most people feel comfortable when the environment temperature is 22oC. The relative humidity also has a considerable effect on comfort as it affects the amount of heat a body can dissipate through evaporation.

Relative humidity is a measure of air’s ability to absorb more moisture. Most people prefer a relative humidity of around 50%. Air motion is another important factor that affects human comfort, it removes the warm moist air that builds up around the body and replaces it with fresh air. Air motion aids the heat rejection of a body by both convection and evaporation. It is important to strike a balance between having air motion strong enough to remove the heat and moisture from around a body but not strong enough to be felt as a breeze as this could cause discomfort. An airspeed of 0.25m/s is gentle enough to go unnoticed but strong enough to remove the heat and moisture. Other factors that affect comfort are air cleanliness, odour and noise. Therefore the goal of air conditioning is to maintain these factors at the desired levels. This is achieved using air conditioning units, in its simplest form, one that only heats or cools the air, a simple refrigeration cycle is used which utilises an evaporator, a condenser, an expansion valve, a compressor, some piping to connect them all, some refrigerant and some fans.

In cooling mode the refrigerant in liquid form passes through the expansion valve and into the evaporator, a fan blows air over the evaporator allowing the refrigerant to absorb heat from the air, in order for it to become gaseous, thus cooling the air. The refrigerant then passes through a compressor into the condenser; here it rejects the heat to the atmosphere and returns to a liquid state. In heating mote the process is reversed, where the evaporator acts like a condenser and the condenser becomes the evaporator. In more sophisticated systems the evaporator and expansion valve are contained in a standalone unit termed an indoor unit, this unit is placed in a room that needs air conditioning and is connected to an outdoor unit by copper piping. The outdoor unit contains the compressor and condenser and is generally located outdoors on a rooftop or on the side of the building. This arrangement is called a split system. The indoor unit usually has a filter that will clean the air that passes through it, a fan that can be controlled to adjust the speed of the air and a control that can adjust the amount of heating or cooling provided depending on the unit chosen.

Split systems are generally used in single room applications such as comms rooms. Multi-split systems are an extension of normal split systems and feature a greater number of indoor units connected to a single outdoor unit. The number of indoor units is generally between two and four. In such an arrangement all indoor units must be in the same mode; either heating or cooling. Multi-split systems can be utilised in a duty/standby mode. Variable Refrigerant Flow also known as Variable Refrigerant Volume.This is an extremely efficient, reliable, energy saving way to heat and cool all types of buildings with minimum installation time or disruption. The volume or flow rate of refrigerant is accurately matched to the required heating or cooling loads thereby saving energy and providing more accurate control. In short, it is probably the best systems currently available for mid to large applications. The term VRF generally refers to an air conditioning system that connects multiple indoor units to single outdoor condensing unit.

The refrigerant flow is controlled by inverter controlled variable speed compressors to fulfil your cooling or heating requirements. VRF systems generally come in two varieties; 3-pipe systems allow for simultaneous heating and cooling of indoor units, whereby the excess heat from one room can be used to heat another room in a different part of the building. In this system the refrigerant is provided in all three phases by the outdoor unit. Using this method conserves energy as it is not wasted to the atmosphere. In a two-pipe system all the indoor units must be in the same mode, either heating or cooling, simultaneous heating or cooling is not available. Two pipe systems are generally used in areas where all the indoor units are located in the one room, such as a shop floor for example, where only one mode of heating will be required. Two pipe systems are also used as a cooling only system where the heating is provided by a different system i.e. under-floor heating. A sophisticated control system enables switching between the heating and cooling modes In more sophisticated versions, the indoor units may operate in heating or cooling mode independently of others This latter arrangement offers potential energy savings when heating and cooling are required simultaneously in different zones This type of system requires no internal plant room space and offers great flexibility through the many types of air handling units available Applications vary from office

, retail, hotel, luxury apartments, industrial, new and retrofitted buildings. Standard outdoor condensing units are powered by electricity, in a GHP system the outdoor unit is powered by a gas engine. This system uses clean burning natural gas for a highly effective operation with very limited use of electrical power. It has a number of advantages over the standard electric VRF: An air handling unit or AHU is a device used to provide conditioned air as part of a heating, ventilation or air conditioning system. The basic function of an AHU is to remove stale air from the rooms of a building and replace it with conditioned air. Air handling units are usually made up of: The AHU is connected to ductwork that distributes the air around the building; it can also extract the air back to the AHU and exhaust it to the atmosphere. There are a wide range of features and configurations available to suit your air conditioning requirements so that Air can be supplied at the required temperature, humidity, volume etc.

Small air handlers, for local use, are called fan coil units, and may only include an air filter, coil, and fan. A heat recovery unit is a device that removes stale air while keeping the heat in. it operates on a principle similar to an air-handling unit. Two fans are used, one to remove stale air from the room and the other supplies fresh air from outside. The two air streams pass through a heat exchanger, in which the heat from the stale air is transferred to the fresh air. Up to 95% efficiency can be demonstrated. A chiller is a machine that removes heat from a liquid via a vapour compression or absorption refrigeration cycle. Generally the liquid being chilled is water; which can then be used in the cooling of machines and other industrial equipment. A water chiller is a complete system filled with refrigeration equipment, including a condenser, refrigerant, pipes, coolant expansion reservoir, pumps, and so on. In air conditioning systems, chillers can be used to distribute chilled water to the cooling coils of fan-coil units, where it can be used to cool the air.