1 Heating, ventilation and air conditioning
2 Heating, ventilation and air conditioningTraditionally, non-industrial ventilation systems commonly known as heating, ventilating and air-conditioning (HVAC) systems were built to control temperature humidity odours
3 Background informationThere are different systems and methods for ventilation depending on the requirements. How the temperature and the air rate are regulated, depend on the ventilation system.
4 Facts Approximately 30% of the energy delivered to buildings is dissipated in departing ventilation and exfiltration air streams. In buildings constructed to very high standards of thermal insulation the proportion of airborne energy loss can be much higher. The amount of energy consumed depends on the flow rate of ventilation amount of conditioning air to achieve thermal comfort (heating and cooling) operation of mechanical ventilation systems required humidity.
5 Components of a ventilation systemA ventilation system consists of the following components: Fans Air-cleaning and filtration systems Heating, cooling and humidification systems Heat recovery systems Recirculation of indoor air Control system Click on the components to get more information A ventilation system consists of different components. All components are important when discussing energy efficiency. Many of the components are selected during the design phase, but during the operation phase maintenance and movement of components often occur.
6 Fans Fans are used in ventilating units to transport the air from various air intakes through the duct system to the room which is to be ventilated. Every fan must overcome the resistance created by having to force the air through ducts, bends and other ventilation equipment. The resistance causes a fall in pressure, and the size of this fall is a decisive factor when choosing the dimensions of each individual fan. Fans can be divided into a number of main groups determined by the impeller’s shape and its operating principle: Radial fans Axial fans
7 Radial fans Radial fans are used when a very high total pressure is required. The particular characteristics of a radial fan are essentially determined by the shape of the impeller blades. There are 4 types: Backward curved Backward angled Straight radial Forward curved Backward curved: The air volume that can be delivered by backward-curved blades varies considerably depending on the pressure conditions. The blade forms makes it less suitable for contaminated air. Up to 80% efficiency is achievable while keeping the fan’s sound levels low. Backward-angled straight blades (P-impeller) - Fans with this blade shape are well suited for contaminated air. Up to 70% efficiency can be achieved. Straight radial blades (R-impeller) - The blade shape prevents contaminants from sticking to the impeller even more effectively than with the P-impeller. No more than 55% efficiency can be achieved with this type of fan. Forward-curved blades (F-impeller) - The air volume delivered by radial fans with forward-curved blades is affected very little by changes in air pressure. The impeller is smaller than the B-impeller, for example, and the fan unit consequently requires less space. An efficiency of approximately 60% can be achieved.
8 Axial fans The simplest type of an axial fan is a propeller fan. A freely rotating axial fan of this type has a very poor efficiency rating, so most axial fans are built into a cylindrical housing. Efficiency can also be increased by fitting directional vanes immediately behind the impeller to direct the air more accurately. The efficiency rating can be 75% without directional vanes and up to 85% with directional vanes. Another type of axial fan is a cross-flow fan where the air flows straight across the impeller, and both the in and out flow are in the periphery of the impeller. In spite of its small diameter, the impeller can supply large volumes of air and is therefore suitable for building into small ventilation units, such as air curtains for example. Efficiency of up to 65% can be achieved
9 Efficiency of fans Fan connections to the inlet and outlet must be designed in a specific way to avoid losses. As a rule of thumb it can be said that the duct diameter on the inlet side must have the same size as the inlet duct diameter on the pressure side (outlet) must be 3 times larger than on the inlet.
10 Efficiency of fans Radial fans must be at least 5 times larger on the suction side (inlet), and the same size as the duct diameter on the pressure side (outlet). If the connections are different to this there could be a greater pressure reduction. This extra pressure drop is called the system effect or system dissipation, and can cause the fan to produce a smaller volume of air.
11 Specific Fan Power There are now stringent requirements to ensure that power consumption in a building is as efficient as possible so as to minimise energy costs. Specific Fan Power (SFP) has been introduced as a measurement of a ventilation system’s energy efficiency. The Specific Fan Power for an entire building can be defined as the total energy efficiency of all the fans in the ventilation system divided by the total air flow through the building. The lower the value, the more efficient the system is at transferring the air. The smaller the specific fan power, the less electricity will be needed to transport 1m3 of air. Typically the SFP should be 3-4 for large systems and 5-7 for small units.
12 Specific Fan Power To calculate the SFP the following information is required: Power of all fans in the system (kW) Volume flow of air in the system (m3/s) SFP = P/V (kW/(m3/s)) To obtain the power of all fans it is necessary to read the kW- rating which can be found on the information plate on the electric motors (which drive the fans in your system). To obtain the volume flow you can find the rated volume flow on each fan in the documentation for the ventilation system. Elsewhere an expert can measure the volume flow with appropriate instrument.
13 Air-cleaning and filtration systemsThere are two reasons for using filters in an air-handling unit: To prevent impurities in the outside air from entering the building. To protect the unit’s components from contamination. The filter’s capacity to trap particles is called its Dust Holding Capacity and filters are often divided into three classes depending on this capacity: Coarse filter EU1 to EU4 Fine filter EU5 to EU9 Absolute filter EU 10 to EU 14.
14 Air-cleaning and filtration systemsBoth glass fibre and synthetic materials are used for filters. It appears that glass fibre filters maintain a better Dust Holding Capacity throughout their working life. It is important to protect the filter from moisture as this can alter the characteristics of the filter fibres and impair its Dust Holding Capacity. Glass fibre filters are more susceptible to the effects of moisture than synthetic filters.
15 Heating batteries Where the outside air is colder than the required temperature for the supply air it is necessary to warm the air before it enters the building. The air can be warmed in a heating battery, by using either an electric heating battery or a hot water battery.
16 Electric heating batteriesAn electric-heating battery consists of a number of enclosed metal filaments or wire spirals. They create an electrical resistance which converts the energy to heat. The advantages of the electric battery are: It has a small pressure drop. It is easy to calculate the power to the battery. It is inexpensive to install. The main disadvantage is: The metal filaments have considerable heat inertia so the electric battery has to be fitted with overheating protection.
17 Water heating batteriesCrossflow water-heating batteries are the most common type of water-heating batteries in ventilation units. The water flows at right angles and in the opposite direction to the air stream. The water flows upwards through the battery. This allows any air bubbles to collect at the highest point where they can be easily drawn off via a ventilating pipe.
18 Heat recovery systems In a ventilation unit it is often economical to attempt to recover the heat which is contained in the exhaust air and use it to warm the supply air. There are several methods for achieving this type of heat recovery: Plate heat recovery. Rotary heat recovery. Battery heat recovery. Chamber heat exchanger. Heat pipe.
19 Plate heat recovery The exhaust air and supply air pass on each side of a number of plates. The exhaust and supply air should not normally come into contact with each other. There may be some condensation in a plate heat recovery unit so they need to be fitted with condensation drains. Because of this condensation there is also a serious risk of ice formation, so some type of defrosting system is also needed. Heat recovery can be regulated by means of a bypass valve which controls the intake of exhaust air. Efficiency: 50-85%
20 Rotary heat recovery Heat is transferred by a rotating wheel between exhaust and supply air. This system is open and there is a serious risk that impurities and odours will be transferred from the exhaust to the supply air. To some extent this can be avoided by positioning the fans in the correct way. The degree of heat recovery can be regulated by increasing or decreasing the rotational speed. There is little risk of freezing in the heat recovery unit. Efficiency: 75-90%
21 Battery heat recovery Water, or water mixed with glycol, circulates between a water battery in the exhaust air duct and a water battery in the supply air duct. The liquid in the exhaust air duct is heated so that it can transfer the heat to the air in the supply air duct. The liquid circulates in a closed system and there is no risk of transferring impurities from exhaust air to supply air. Heat recovery can be regulated by increasing or decreasing the water flow. Efficiency: 45-60%
22 Chamber heat recovery A chamber is divided into two parts by a valve. The exhaust air first heats one part of the chamber, then the valve changes the air stream so that the supply air is heated by the warmed-up part of the chamber. Impurities and odours can be transferred from exhaust air to supply air. Efficiency: 80-90%
23 Heat pipe This heat recovery unit consists of a closed system of pipes filled with a liquid that vaporises when heated by the exhaust air. When the supply air passes the pipes, the vapour condenses back into liquid again. There can be no transfer of impurities. Efficiency: 50-70%
24 Recirculation of indoor airRecirculation is normally used when the ventilation system functions as heating in a building or a part of a building. It is difficult to obtain good indoor air quality using recirculation. Recirculation should incorporate air cleaners a by-pass or auxiliary exhaust system regular maintenance and inspection devices to monitor system performance The system should remove as much of the contaminant as can economically be separated from exhaust air.
25 Control systems Ideally, buildings should have minimal HVAC (Heating Ventilation Air Conditioning) systems. However, most modern urban buildings, with their location and building constraints, require more extensive electrical and mechanical systems with automatic control.
26 Control systems The best control strategy allows occupants to directly manipulate simple and understandable building features, such as windows or shades. Controls should provide immediate feedback on their effects. Controls should not require occupant attention for safe, healthy indoor conditions, low energy consumption and operating costs. Automatic building controls must ensure the building operates efficiently regardless of occupant behaviour.
27 Ventilation systems - overviewThere are five basic types of ventilation systems: Dilution and removal by general exhaust. Local exhaust. Replacement or makeup air. HVAC, primary for comfort. Recirculation systems. Ventilation systems generally involve a combination of these types of systems.
28 Why ventilate Ventilation is needed to maintain good indoor air quality by diluting and removing pollutants emitted within a space. It should not be used as a substitute for proper source control of pollutants. Ventilation is additionally used for cooling and (particularly in dwellings) to provide oxygen to combustion appliances. Good ventilation is a major contributor to the health and comfort of building occupants
29 How does ventilation workVentilation is accomplished by introducing 'clean' air into a space. This air is either mixed with the air already present in the enclosure to give 'mixing' or 'dilution' ventilation, or is used to 'displace' air in the space to give 'displacement' or 'piston flow' ventilation. These techniques give characteristically different pollutant profiles.
30 Types of ventilation In general there are 2 types of ventilation:Natural ventilation. Mechanical ventilation (including mixing and displacement ventilation).
31 Natural ventilation In the past natural ventilation dominated.Its advantages include simple components low investment costs. The disadvantages include poor control of ventilation poor heat economy.
32 Natural ventilation In the past natural ventilation dominated.Advantages include simple components low investment costs negligible operating costs. Disadvantages include poor control of ventilation temperature variations not as effective during warm, humid summer months difficult to retrofit in buildings poor heat economy.
33 Natural ventilation There are many office buildings throughout Europe that rely on natural ventilation to meet all their cooling needs. In North America, there is a trend towards natural ventilation and many new buildings have operable windows. Elimination or avoidance of mechanical air conditioning is difficult in hot humid climates but is possible in most other climates.
34 Mechanical ventilationMechanical ventilation systems are capable of providing a controlled rate of air change and respond to the varying needs of occupants and pollutant loads. In general incoming supply air is filtered and some systems have provision for heat recovery from the exhaust air stream. The potential advantages of mechanical ventilation, especially for smaller buildings, can often be outweighed by installation and operational cost, maintenance needs and inadequate return from heat recovery. Mechanical ventilation is often essential in large office buildings where fresh air must penetrate to the centre of the building and high heat gains can cause over heating. Several configurations of mechanical ventilation are possible: Supply ventilation Extract (or exhaust) ventilation Balanced (supply extract) systems
35 Supply ventilation A fan blows air into the room/building from outside. There will be a positive pressure in the room/building. Extract ventilation A fan extracts air out of the room/building. There will be a negative pressure inside the room/building. Balanced ventilation A combination of supply and extract ventilation. This is often combined with heat recovery to utilise the heat or cooling of the extracted/supplied air
36 Types of mechanical ventilationTwo types of mechanical ventilation are in use: Mixing ventilation - In mixing ventilation the supply air is distributed at a high outlet velocity and mixed with the ambient air. The air that reaches the occupied zone is a mix of supply and ambient air. Displacement ventilation - In displacement ventilation, cool supply air is distributed at low velocity at floor level to the ventilated space. A fresh and pure supply air reaches the occupied zone without any significant mixing of warm or contaminated ambient air.
37 Displacement ventilationAdvantages of displacement ventilation systems over conventional air conditioning and mixed flow systems: Cost effective to run. Good operational efficiency. Wide site application. Extremely quiet in operation. Good compatibility with architectural requirements.
38 Displacement ventilationDisplacement ventilation offers significant cost and operational advantages for indoor climate control, by providing controllable supply air volumes at low velocities throughout a wide variety and size of occupied zones – without creating cold air draughts. A key feature of displacement ventilation is that the methods and locations of supply air entry, and air extraction, can be discreet – compatible with both the architectural design and critical noise level requirements. Applications are as varied as galleries, restaurants, concert halls, factories, foyers, airport lounges or shopping malls
39 Ventilation rates The quantity of ventilation needed depends on the amount and nature of contamination present in a space. To determine the overall ventilation needed, it is useful to identify the dominant pollutant. This is the pollutant that requires the greatest amount of ventilation for removal. To assess the emission from the processes one can ask people working near the processes if they smell, feel or in any other way have a problem with the emissions. The methods to measure the emission vary from component to component and is often a job for specialists to investigate
40 Example Ventilation ratesExamples of minimum rates are given in the following table: Ventilation rates are specified in EN15251
41 Evaluating the energy consumptionheating the air tranportation of the air You will often see that the amount of energy for heating and transportation are at the same level Energyfor heating depends on: Air volume Temperature of outdoor and indoor air Heat recovery Working hours Energy for tranportation depends on: Input power to fans
42 Evaluating the energy consumptionHow to find data for the energy consumption
43 Evaluating the energy consumptionA. Heating: You find the energy consumption with the following formula: E [kWh] = (c x ) x [m3/s] x [ C] x (1 – ŋ) x [h] (c x ) = 1,21 kJ/m3xC B. Air transport: E [kWh] = [kW] x [h]
44 Example „energy consumptionA. Basic data - Heating: Air volume: 2.4 m3/s Temperature outdoor yearly average: + 8 C Temperature indoor set inlet: + 20 C Heat recovery efficiency: 0.7 Working hours: 60 hours/week x 52 weeks = 3120 h Energy consumption for heating: 1.21 [kJ/m3xC] x 2.4 [m3/s] x (20 – 8) [ C] x (1 – 0.7) x 3120 [h] E = kWh
45 Example „energy consumptionB. Basic data - Air Transport: Power input fan motors: 8 kW Working hours: 60 hours/week x 52 weeks = 3120 h Energy consumption for air transport: E = 8 [kW] x 3120 [h] E = kWh
46 Example „energy consumptionEnergy consumption for heating: kWh Energy consumption for air transport: kWh Total energy consumption: kWh
47 Making energy savings The energy used in ventilation is a product of power (kW) and time in hours (h). The main issues are to reduce either the amount of the power or the operating hours the power is on. In reducing both power and operating hours care is needed not to change the indoor air quality that would be unacceptable to staff. Energy savings can be made: Switch it off Slow it down Select components with best efficiency Use a control system
48 Energy savings - 1. Switch it offThe simplest method of reducing energy is to switch it off when it is not needed. There are several ways of controlling “switching off” Manual switching off Time switch Demand controlled ventilation Control system
49 Energy savings - 1. Switch it offThe simplest method of reducing energy is to switch it off when it is not needed. There are several ways of controlling “switching off”. Manual switching off ...of the fan or the ventilation system: This method is the cheapest because no investment is needed. Because it relies on people it can be the least reliable method. Examples: Switching off at lunchtimes, breaktimes etc. Time switch Demand controlled ventilation Control system
50 Energy savings - 1. Switch it offThe simplest method of reducing energy is to switch it off when it is not needed. There are several ways of controlling “switching off”. Manual switching off Time switch ...on the fan or the ventilation system: For use in special areas or rooms with different times of use or occupancy than the rest of the building (or system). Example: Meeting rooms. Demand controlled ventilation Control system
51 Energy savings - 1. Switch it offThe simplest method of reducing energy is to switch it off when it is not needed. There are several ways of controlling “switching off”. Manual switching off Time switch Demand controlled ventilation: Air flow rate is governed by a presence sensor. If no people are present the system will switch off after a defined period. Control system
52 Energy savings - 1. Switch it offThe simplest method of reducing energy is to switch it off when it is not needed. There are several ways of controlling “switching off”. Manual switching off Time switch Demand controlled ventilation Control system: Make settings in the building control system for the periods when the system should be turned off. Often this could be done in the overall building management system.
53 Example Ventilation ratesOffice building 2000 m2 Heating capacity for ventilation 45 kW Ventilation On 24 hours a day, 7 days a week (168 hours weekly) Heat recovery 0 % Energy consumption kWh (100%) Switch off 12 hours 5 days (Mon-Fri) 18 hours 1 day (Sat) 24 hours 1 day a week (Sun) From 168 to 66 hours weekly Switch off for 102 hours Energy consumption kWh (40%) Energy savings kWh (60%) We should also consider the energy to the electric motors which drive the fans. This will show similar percentage energy savings
54 Energy savings - 2. Slow it downInstead of switching the system off, the ventilation system can reduce the ventilation rate without a noticeable change to the indoor climate. Savings can easily be achieved by reducing the air flow rate.
55 Example Ventilation ratesOffice building 2000 m2 Ventilation On 24 hours a day, 7 days a week (168 hours weekly) Heat recovery 0 % Energy consumption kWh (100%) Slow it down On 24 hours a day, 7 days a week (168 hours weekly) Reduced air rate From m3/h to 7000 m3/h Energy consumption kWh (40%) Energy savings kWh (60%)
56 Energy savings – 3. Select components with best efficiencyAll of the following components are important when discussing energy efficiency: Fans: The efficiency of fans can be 80-85%, but inappropriate choice and/or dimensioning of a fan can result in an efficiency of under 50%! Air cleaning and filtration As well as ensuring that the filters are in good condition the individual components of the whole system need to be cleaned regularly. For example the efficiency of a heat recovery unit which is covered with dust will decrease from 80% to 20%. Heat recovery and equipment Ensure that the heat recovery system is functioning as planned.
57 Energy savings – 4. Use of control systemsThe potential energy saving gained from controllers can be up to 60% of ventilation energy costs, depending on Building type and use Local climate Control systems are:
58 Cooling Particularly in large commercial office buildings, high heat loads are developed through lighting, computing and other electrical sources. Further heat gains are derived from occupants, solar radiation and high outdoor temperatures. These factors make cooling of the indoor air essential. The choice is either to introduce mechanical cooling or to introduce ventilation cooling. In either case heat gains should be minimised by good building design and reduced power consumption. Mechanical cooling is energy intensive and contributes to peak power loads. When mechanical cooling is needed, ventilation must be minimised to prevent the unnecessary loss of conditioned air.