Flow describes the volume of liquid pumped within a given period of time. The physical size of a pump determines the flow, which can pass through it. Thus flow will always be an issue when you select a pump.
Technically head means meters of water column. It indicated how high a given pressure can lift a column of liquid. Knowledge of the relationship between flow and head and about the conversion between head and pressure will enable you to perform basic sizing of a pump for a specific application.
Head is defined as a universal measurement of pump performance independent of the liquid, whereas pressure can be defined as an adapted measurement of pump performance; adapted to the actual liquid and situation.
Density expresses how heavy a liquid, gas or solid is. Pumping of liquids with different densities affects the power input of the pump. The higher the density, the higher the power input. It is therefore important to know the density of the pumped liquid when selecting a pump.
Viscosity is commonly perceived as ‘thickness’, or resistance to pouring. Viscosity describes a liquid’s internal resistance to flow and may be thought of as a measure of liquid friction. Thus, water is ‘thin’; having a low viscosity, whereas vegetable oil is ‘thick’ and therefore has a higher viscosity. Viscosity affects the selection of pump type and motor size as a highly viscous liquid is harder to pump than a liquid with a low viscosity.
When focusing on power in connection with pumps, it is often in relation to the power consumption of a pump. This factor can be decisive for the choice between two almost similar pumps. Power is also used for the calculation of efficiency, pump size and motor size.
Pumps and Pump Operation
Keeping performance up over the products entire life – choosing the most energy efficient solution sets the foundation for dramatic savings on operating costs. High-efficiency motors, electronic speed control and state of the art hydraulic efficiency are all measures that can be taken to drive down operating costs. Pumps and pump operation is the core of the Grundfos world.
Imagine that you drive a car and you regulate the speed of the car by stepping on the brakes while you keep stepping on the speed. This will not only cause the motor to hesitate but it will also use a lot of fuel.
Most people will agree that this is not a good way to drive the car. Nevertheless, this is how most pumps in the world are regulated. Often a standard pump is installed and a valve is used to regulate the pump performance. It’s simple and it works, but it is very inefficient.
Cavitation occurs when the pressure of a liquid at a constant temperature falls below its saturated vapour pressure point (or boiling point). The figure shows the curve for saturated water vapour pressure as a function of the temperature (in this case, the liquid is water).
ATEX is an abbreviation of a French term used to denote an explosive atmosphere
An abrasive liquid contains substances, often minerals or inorganic substances, that are harder than the material
In wastewater transport and treatment aerobic means that oxygen is available and that it can be used as an oxidation agent in the degradation of organic matter. Under aerobic conditions oxygen (O2) is present. This is in contrast to anaerobic where no oxygen is present. In wastewater transport and treatment aerobic means that O2 is available and that it can be used as an oxidation agent in the degradation of organic matter. Products of this process are CO2 and H2O.
BTU (British Thermal Unit)
The British thermal unit (BTU) is a unit of energy used in the power, steam generation, heating and air-conditioning industries. In scientific contexts the BTU has largely been replaced by the SI unit of energy, the joule [J].
The British thermal unit (BTU or Btu) is a unit of energy used in the power, steam generation, heating and air-conditioning industries. Although it is still used ‘unofficially’ in metric English-speaking countries (such as USA, Canada, UK), its use has declined or has been replaced in other parts of the world. In scientific contexts the BTU has largely been replaced by the SI unit of energy, the joule [J].
The capacity of small cooling systems and heat pumps is often given in BTUs – meaning the number of BTUs per hour, i.e. BTU/h.
One British Thermal Unit (BTU) is the amount of energy required to raise the temperature of a pound of water by one degree Fahrenheit.
1 BTU = 1.055 kJ.
1 BTU/h = 0.293 W.
The flow of piped medium in the direction opposite to normal flow is called backflow. It is caused by a difference in water pressures.
Backflow is normally prevented by a non-return valve, and sometimes a gooseneck on the pipe system. In the pictured system, only the gooseneck will prevent backflow into the basement.
The term baffle covers a flat board or plate, deflector vanes, guides, grids, gratings or similar devices constructed or placed in flowing water, wastewater or slurry systems.
A baffle is used to absorb energy to slow the flow or to produce a more uniform distribution of velocities. It can divert, guide or agitate the liquid, and it can check eddies.
In any thermal heat exchange process, a mixture of two energy flows will result in a new stage or phase called the balance point. The mixture of hot and cold water in a tap is a brilliant example of a balance point. It requires the adjustment of two flows to achieve a required temperature. The balance point can be illustrated by a simple formula stating the energy flux for each of the two flows.
mbalance X cbalance X tbalance = mhot X chot X thot + mcold X ccold X tcold
A buffer tank is a storage tank used on the cold user side of an air-conditioning system. The system can be the secondary side of a traditional compressor-driven system or a free-cooling system, where perhaps cooling only occurs at night. The buffer tank is a container in which the cooled medium can be stored.
A buffer tank is typically used when there is a variable cooling requirement. In such applications the tank is used as storage to cover peak loads or in situations when a surge in demand exceeds the capacity of the cooling system.
When a cooling system starts up, it increases energy consumption and wear on the cooling compressor, in comparison to continuous operation. A buffer tank is well-suited to situations where cooling loads are small because it reduces the number of starts and thus decreases wear and energy consumption.
A butterfly valve is from a family of valves called quarter-turn valves. The “butterfly” is a metal disc mounted on a rod. When the valve is closed, the disc is turned so that it completely blocks off the passageway. When the valve is closed, the disc is turned so that it completely blocks off the passageway.
When the valve is fully open, the disc is rotated a quarter turn so that it allows an almost unrestricted passage of the process fluid. The valve may also be opened incrementally to regulate flow. Unlike a ball valve, the plate is always present within the flow, therefore a pressure drop is always induced in the flow regardless of valve position.
The butterfly valve derives its name from the way a “butterfly-shape image” appears to form as it turns.
The butterfly valve is widely used in the chemical industry, wastewater systems and water supplies.
The valve is designed so that the flowing medium does not have to come in contact with the valve’s moving metal parts. The valve seat can be made from many different kinds of material to cater for every kind of medium.
A butterfly valve is very robust and requires very little maintenance.
Butterfly valves are usually available in medium large to very large sizes (DN 40–600).
Pipe connection between the suction and discharge side of a booster set in order to bypass water when the pumps are not in operation.A bypass connection is a pipe diversion consisting of a manifold, two isolating valves and a non-return valve. The diversion is placed between the suction and discharge manifold of a booster set.The bypass connection allows water to bypass the pumps from the suction to the discharge manifold. The bypass connection is mostly used in applications where the inlet pressure is positive, so that it is possible to supply water from the mains if the booster set is out of operation.
A channel impeller works directly on the pumped liquid with the liquid passing through the impeller itself. A channel impeller can be described as a closed, semi-open or open impeller.
A channel impeller works directly on the pumped liquid with the liquid passing through the impeller itself. A channel impeller can be described as a closed, semi-open or open impeller.
The impeller can have one or more channels of varying size allowing for free passage of impurities up to a particular size. In impellers with more than one channel, fibrous impurities might get caught on the leading edges of the vane, causing the pump to clog.
Channel impellers can have efficiencies as high as 80-85%. Liquid with a high sand content will cause problems with impeller clearance on a channel impeller.
A compensator can be built-into a heating system to absorb pipe linear expansion as an alternative to an expansion loop. Pipe linear expansion in a heating system is caused by the difference between the operating temperature and ambient temperature and by variations in media temperature. A compensator can be built-into the system to compensate for this linear expansion, as an alternative to an expansion loop. The compensator can be a hinged or axial type. Pipe fixtures and lateral pipe guides have to be built-in if a compensator is used to deal with the expansion.
A hinged compensator allows a pipe corner to move, so that the pipe expansion can be absorbed by the compensator. An axial compensator works by allowing two pipes to move against each other, thus absorbing the expansion. A flexible bellow prevents the system from leaking.
District heating systems often use an alternative to compensators. Instead, pipes are stressed/distorted in such a way that any expansion is minimised. To deal with expansion, stressed steel pipes and even extra-strength steel pipes are used as an alternative or in a combined solution.
A condensate pump is used to pump condensed water in cooling systems. Condensation must be removed when it forms on cooling surfaces and in cooling systems. The condensate should be collected in a drip tray. If the condensate cannot be drained away from the drip tray by gravity, a condensate pump is fitted.
A condensing boiler is provided with a condenser, by which the water vapour produced by the burning of gas or oil in the boiler, condenses back into liquid water – hence the name “condensing boiler”. The energy contained in the vapour, would without a condenser, normally discharged to the atmosphere through the flue.
A condensing boiler is a boiler provided with a condensing device designed to recover energy normally discharged to the atmosphere through the flue.
When a condensing boiler is working at peak efficiency the water vapour produced by the burning of gas or oil in the boiler condenses back into liquid water – hence the name “condensing boiler”. The boiler uses a heat exchanger so that incoming air or water cools the exhaust, forcing the condensation of the water vapour it contains; this heats the incoming air (if an air-to-air heat exchanger is used) or pre-heats the water (if an air-to-water heat exchanger is used).
A small proportion of the extra efficiency of the condensing boiler is due to the cooling of the exhaust gases, but the majority of the energy recovered is from the condensation of the water vapour in the exhaust gases. This releases the latent heat of vaporisation of the water – 2260 kJ/kg (970btuh/pound) of condensate, i.e. the water vapour released whenever one burns fossil fuels.
The actual operating efficiency of a condensing boiler depends on the ambient air temperature and the relative humidity. If the incoming air is at 100% relative humidity, the condensing boiler will operate at its maximum efficiency, as it can condense all the extra water vapour introduced by combustion. As the relative humidity falls, so will the actual efficiency of the condensing boiler, because less of the water vapour produced can be recovered from the exhaust.
Cross Flow Heat Exchanger
A cross-flow heat exchanger exchanges thermal energy from one airstream to another in an air handling unit (AHU). Unlike a rotary heat exchanger, a cross-flow heat exchanger does not exchange humidity and there is no risk of short-circuiting the airstreams.
A cross-flow heat exchanger is used in a cooling and ventilation system that requires heat to be transferred from one airstream to another. A cross-flow heat exchanger is made of thin metal panels, normally aluminium. The thermal energy is exchanged via the panels. A traditional cross-flow heat exchanger has a square cross-section. It has a thermal efficiency of 40–65%. A counter-flow or dual cross-flow heat exchanger can be used if greater thermal efficiencies are required – typically up to 75–85 %.
In some types of exchanger, humid air may cool down to freezing point, forming ice. A cross-flow is typically less expensive than other types of heat exchanger. It is normally used where hygienic standards require that both airstreams are kept completely separate from one another. It is often used in heat recovery installations in large canteens, hospitals and in the food industry. Unlike a rotary heat exchanger, a cross-flow heat exchanger does not exchange humidity.
A DX system is a cooling system where the primary coolant is used for evaporation. DX systems are typically used with very small, stand-alone systems, but they can also be used in large industrial cooling systems.
A detention tank is an artificial flow-control structure that is used to contain stormwater and wastewater for a limited period of a time. The detention tank can be incorporated into the sewer network system at the wastewater treatment plant or at factories.
A detention tank in the sewer network is used to even out peak flows in the system. This helps to avoid overflow into the recipient, protecting downstream areas. It also helps to prevent hydraulic overload of downstream sewers and wastewater treatment plants.
At the wastewater treatment plant the detention basin is used to even out fluctuations in the wastewater inflow to ensure an even flow throughout the process tanks at the plant. This is necessary to keep the treatment processes operating in an optimal way, to maintain discharge requirements and to avoid sludge drift.
Factory detention tanks (more commonly equalisation tanks) are also used to even out peak flows. Additionally, they are used to stabilise batch volumes of process water with regard to pH or chemical substances before discharge into the sewer system.
The dew point temperature is the temperature where the water content in the air condenses into water. This means that the water content in the air changes states from gas to liquid.
The dew point is related to the relative humidity. When the relative humidity increases, the difference between the dew point temperature and the air temperature decreases. When the relative humidity is 100%, the air temperature and dew point temperature are the same.
The dew point temperature is used for example during dimensioning of cooling and ventilation systems to avoid build up of water and ice on the cooling surface. If the air is cooled on a cooling surface, then the cooling surface temperature must be higher than the dew point temperature to avoid condensate from forming.
Differential pressure regulating valve
Differential pressure regulators are built into the system where a constant differential pressure is desired. They are often installed at the connection point between a district heating system and a consumer building. This ensures that there is a constant differential pressure available for the building’s heating system.
This protects the building’s installation against the differential pressure variations that arise in the district heating distribution network and thus makes it possible to perform an accurate dimensioning of the heating system.
Differential pressure regulators can also be mounted so they create a constant differential pressure across regulating valves. In this way, a valve authority of 100 % for the regulating valve can be achieved, as it is independent from the pressure relationships in the rest of the system. This ensures optimal regulation of the unit relying on the valve. A mixing loop is an example such a unit.
Discharge flow is the assumed flow from discharge units. Normally, it refers to the flow entering a pumping station. It is typically expressed in litres per second or cubic metres per hour.
EN 12056-2 gives some figures and rules on how to calculate discharge flow from buildings of different kinds. The calculation is also part of the sizing program in Grundfos WebCAPS and WinCAPS.
The discharge flow changes during the day depending on building usage. This is called the daily profile or discharge pattern. For dimensioning purposes, always use the peak flow in the daily profile.
n a closed, pressurised system with a circulating media, the total pressure consists of two elements; a static pressure and a dynamic pressure. The dynamic pressure indicates the amount of the total pressure that results from the media’s velocity in the pipes.
The dynamic pressure indicates the amount of the total pressure that results from the media’s velocity in the pipes. The dynamic pressure is calculated using the following formula:
pd = 0,5 x ρ x v²
ρ (rho) = the density of the media
v = mean velocity in the pipe.
The dynamic pressure is used for calculating pressure loss in pipe systems.
Enthalpy is a description for an amount of energy, and can be found in reference material for different elements at different temperatures and pressures. Enthalpy is often given as kJ/Kg.
Enthalpy, typically denoted by H, is a state defined as
H = U + p • v.
Enthalpy H is given in Joule (J)
U = inner energy; given in Joule (J)
p = pressure; given in pascal (Pa)
v = volume; given in cubic metres (m3).
The inner energy in, for example a gas, is an expression of the movement of the gas molecules. If heat is added to a gas, the inner energy will increase.
Enthalpy is thus a description for an amount of energy, and can be found in reference material for different elements at different temperatures and pressures. Enthalpy is often given as kJ/Kg.
In ventilation and cooling systems, air changes state all the time. A Mollier’s diagram can be used to acquire an overview of these different state changes. Different types of Mollier’s diagrams are available for different purposes and situations.
Enthalpy is an expression of the energy/work that is necessary for a process.
Steam at a pressure of 1 bar is heated from 200 ºC to 400 ºC. At 200 ºC, steam has one particular enthalpy, and another at 400 ºC. This difference in enthalpy measures how much heat (energy) needs to be added for the steam to achieve this temperature increase.
Exfiltration refers to the leakage of wastewater into soil and groundwater through faulty joints, damaged pipes, around manholes, etc. The problem is difficult to discover, and there is a risk of contamination of the environment, such groundwater, lakes and ponds. Advanced controls can sometimes measure a pressure loss in the pipes downstream from the leakage
Expansion is an expression used in a cooling plant. It relates to the temperature and the process that brings the refrigerant from the condenser side to the evaporator side.
All refrigerants have a liquid, evaporation and gas phase like water at 1 bar: liquid below 100 °C, evaporation at 100°C, and gas (steam) above 100 °C.
The boiling temperature for a refrigerant is pressure dependent, where at a curtain pressure relates to a specific boiling temperature. For example R717 ammonia at 2.9 bar boils at -10°C, whereas at 11.7 bar, it boils at 30 °C.
By expanding the refrigerant into an evaporator through an expansion valve, the refrigerant is brought from one pressure to a lower pressure. It starts to boil and evaporate if the “items” near the evaporator are warmer then the evaporation temperature. The expansion is normally controlled by a thermal expansion valve, securing the required evaporation temperature by expanding more or less refrigerant.
Fin spacing is the distance between fins which are used on air coolers, dry coolers, evaporators and condensers. Decreasing the spacing between fins increases efficiency and it is an inexpensive solution. Therefore the optimum solution is to have as little spacing as possible. A fin spacing of 1.5–5.0 mm is used for dry air cooling. A fin spacing of 3–7 mm is used for humid air where there is a risk of condensation. A fin spacing of 6–20 mm is used in freezer room conditions.
Fluoroelastomers (FKM) are one of the different types of rubber used as a packing material in shaft seals to prevent the pumped media from leaking.
The type of rubber used as packing material depends on the media and pressure in the system. Fluoroelastomer (FKM) covers a whole family of rubbers designed to withstand oil, fuel and a wide range of chemicals, including non-polar solvents. There are standard and special grades; the latter have special properties, such as improved resistance to low temperature operation and chemicals.
FKMs offer excellent resistance to high temperature operation in different types of oil (up to 200°C depending on the grade of FKM). Fluoroelastomer rubbers have limited resistance to steam, hot water, methanol and other highly polar fluids. This type of rubber has poor resistance to amines, strong alkalis and many freons.
The dimension of the free passage usually refers to the largest spherical object that may pass through the impeller. For small and medium-sized sewage pumps, a free passage of 80 mm is normally sufficient. Free passage for large pumps (above 100 l/s) should normally be at least 100 mm. The bigger the free passage, the lower the risk of clogging.
The simple gear pump consists of two spur gears meshing together and revolving in opposite directions within a casing. Any liquid that fills the space between the gear teeth and the case must follow along with the teeth as gear turn.
There are several types of gear pumps. The simple gear pump consists of two spur gears meshing together and revolving in opposite directions within a casing. Any liquid that fills the space between the gear teeth and the case must follow along with the teeth as gear turn. When the gear teeth mesh with the teeth of the other gear, the space between the teeth almost disappears, and the entrapped liquid is forced out the pump. As the gears revolve and the teeth disengage, the space again opens on the suction side of the pump, replenish new quantities of liquid and carrying it around the pump case. As the liquid is carried away from the suction side, a lower pressure is created, which draws liquid in through the suction line.
A large number of teeth on the gears ensures that the media flowing from the pump is homogenous without major pressure spikes. A gear pump with a small number of teeth provides a less homogenous flow, as there are fewer teeth to ensure an even flow. However, pump flow is higher, as the larger spaces between the teeth allow more media to be pumped.
Geodetic head refers to the actual physical difference in height between the liquid level in the pit and the highest point of the discharge pipe or water level in the outlet.
The geodetic head between a pumping station and the outlet from the pumping station will constantly change during a pump cycle. When dimensioning a pump, the average water level between start and stop is normally used for defining the geodetic head.
Here it is important to understand that the geodetic head also can be negative. This will result in the siphoning effect.
Grundfos (large) UPS circulator pump
Grundfos Large UPS is a canned rotor, centrifugal pump for circulating water in heating systems and smaller air-conditioner systems in commercial buildings. These pumps are based on glandless pump or canned rotor technology. The pumped liquid cools and lubricates the motor and rotating parts.
Large UPS circulators are typically used in commercial building like schools, hospitals and office buildings for circulating domestic hot water, heating water and air-conditioning fluid.
The name UPS stands for the German Umwältz Pumpen Selektra, directly translated as Circulator Pumps Selective. S for Selektra indicates that you can select between three speed settings.
The key advantages:
- No maintenance in the pump’s lifetime
- No risk of leakage
- No noise
Three speed settings
For more overview curve information, please download the brochure The Perfect Fit
Grundfos Control MPC – Pump controller
Grundfos Control MPC is a pump controller designed for controlling and monitoring of up to six Grundfos pumps connected in parallel. All pumps must be of the same pump type and size.
Grundfos Control MPC is used for controlling and monitoring of booster systems and circulation systems (HEAC). Control MPC is divided into eight groups based on control variants.
Control MPC consists of a control cabinet with a built-in controller, the CU 351 and all necessary components such as main switch, contactors, IO 351A or -B modules and cabling. In systems with external frequency converters, the frequency converters can be installed in the cabinet.
A heat exchanger is used to transfer heat from one medium to another. This article only describes the transfer of heat from one liquid to another. However, various types of gas to liquid and gas to gas heat exchangers are also common components in HVAC systems.
There are two main types of liquid to liquid heat exchangers:
- Plate heat exchangers
- Tube heat exchangers
Heat exchangers are used in heating systems to separate two media, while at the same time transferring heat from one to the other. An example of this type of application is a heating system with indirect district heating. Here, a heat exchanger is fitted directly after the supply pipe to the building. The heat is transferred from the district heating water on the primary side via the exchanger to the secondary side. Thus, the building’s heating water is never in direct contact with the district heating water.
heat pump is a system that can both cool, heat, and dehumidify air in a room, depending on the demand. These systems have a reversible heat transfer cycle. This means that if the air in a building needs to be cooled, then the evaporator that produces cold air is placed in the building, and the condenser that produces heat is placed outside.
If heat is required inside the building, the process is reversed. The evaporator in the building is used as a condenser (producing heat), with the condenser outside functioning as the evaporator. The process can be reversed whenever necessary.
A heat pump is a good alternative to an electric heating system.
Hot Water Exchanger
A hot water exchanger is used in production of domestic hot water. The hot water exchanger can be connected to a district or central heating system.
Hot water exchangers exist as both bolted plate heat exchangers and soldered plate heat exchangers. Other types of exchangers, such as tube heat exchangers also exist. These are however rarely used in domestic hot water production.
In a plate heat exchanger, the cold water passes the heat-bearing medium through small channels. The two liquids are separated by plates. Counter flow heat exchange is applied, which increases the effectiveness of the exchanger, creating a greater cooling of the heat-bearing medium. Some domestic water exchangers have an extra connection on the secondary side. This allows domestic hot water recirculation to be connected to the exchanger directly.
An impeller is a rotating iron or steel disc with vanes in a centrifugal pump. Impellers transfer energy from the motor that drives the pump to the fluid being pumped by accelerating the fluid radially outwards from the centre of rotation. The velocity achieved by the impeller transfers into pressure when the outward movement of the fluid is confined by the pump casing. Impellers are available as vortex or channel impellers.
The difference between the power induced to the pump and the hydraulic power indicates the efficiency of the pump.
P1 is the total induced power to the pump system. P2 is the power coming from the motor (shaft effect). P2 is the nominal power of the motor.
The difference between P1 and P2 indicates either:
- the efficiency of the motor (ηmot.)
- the efficiency of the motor (ηmot.) + the efficiency of the built-in frequency converter (ηreg.)
P3 is the effect induced to the pump. P3 is mostly equal to P2, because the pump is coupled directly to the motor (no gear or V-belt drive) P4 is the hydraulic power (Q x H).
Infiltration describes the ingress of groundwater into a sewer system through faulty joints, damaged pipes, at manholes, etc. Infiltration increases sewage volume and flow rate, making the sewer and treatment systems more costly.
In places where the pressure pipes are placed below the groundwater level and influenced by gravity the volume from infiltration can be very high. As a result, the pump system has to run faster than it was designed to, which causes more wear and tear and higher energy cost.
In the treatment plant, infiltration will have a negative impact. The process temperature can be lowered, which calls for higher demand of aeration and so on. In separate systems the infiltration can cause capacity problems, increasing the risk of flooding and eventually undermine roads and structures. As a result of the problems caused by infiltration much attention has been focused on renovation of old sewerage systems.
The inlet pressure derives from the pressure of the water supplier or the water pressure created if the booster draws from a break tank. The inlet pressure can be negative or positive; however, negative inlet pressure normally occurs when the booster has to suck water from tanks which are placed below the booster.
The inlet pressure is used for calculating the required boost from the booster pumps as well as the NPSHa (Net Positive Suction Head available). NPSHa is used for determining if a certain pump can be used in a certain application and how the suction pipe is sized.
Sometimes it is necessary to cool the seal faces in a centrifugal pump of single mechanical shaft seals or remove deposits in the seal chamber. In such cases a circulation pipe from the pump discharge side to the seal chamber can be fitted. The cooling liquid flows from the seal chamber back to the pumped liquid. This ensures a good exchange of the liquid in the seal chamber. A pipe dimension of Ø8/Ø10 is sufficient.
The kv value expresses the amount of flow in a regulating valve at a given valve position with a pressure loss of 1 bar. The special situation with a fully open valve determines the kvs value.
The Kvs value expresses the amount of flow in a regulating valve at a fully-open valve position and a pressure differential of 1 bar. The Kvs value is a special case of the Kv value, which indicates the flow at a given valve position and a pressure differential of 1 bar.
Latent Cooling Load
Latent cooling load is a measure of the amount of energy that is necessary to dehumidify the air in a building, for example, regardless of the outdoor humidity. Cooling load needs to be considered when a cooling system is being dimensioned. Latent cooling load refers to the wet bulb temperature. It specifies the cooling capacity a cooling system needs to be able to dehumidify a building to a desired humidity, even when external factors that create humidity are calculated in.
The Greek letter λ, lambda, [W/mK] is used to represent the heat conductivity of a material. The heat conductivity of a material is thus popularly known as its lambda value. The lambda value is used for thermal calculations on buildings and thermal components (insulation, etc.). The thermal conductivity of a material is defined as the quantity of heat transferred in a given time through a distance L,, in a direction normal to a surface area A, due to a temperature difference ΔT, and when the heat transfer is dependent only on the temperature gradient.
Thus, the lower a material’s lambda value, the better its ability to insulate.
n heating and air conditioning systems, water must be distributed from the supply system to the point of consumption. This is done by means of main pumps.
Larger systems can be divided into several pipe circuits with each their local pump. The main pump is the pump that distributes the total amount of water from the supply source.
Due to variations in heat demand and flow in large systems, it is recommended to use speed controlled pumps in parallel as main pumps. By using speed controlled pumps it is also possible to obtain maximum energy savings. A maximum of three pumps plus one standby pump is recommended.
A manometer is an instrument that is used for showing the current pressure in a heating or cooling system at a given location. The pressure is often shown as relative to atmospheric pressure but can be shown as an absolute pressure.
Manometres are installed in those locations where it is necessary to know the pressure level, e.g. a component connection that requires regular pressure-level checks, or the pressure level on either side of a filter to indicate if the filter needs cleaning.
There is often a tendency to fit manometres out of habit and not from any real identified requirement. This means that a large number of pressure gauges are fitted unnecessarily, which takes up servicing and maintenance resources.
The overall energy efficiency of pumps is derived from the usage of motors. The EuP Directive states that from June 16th 2011, motors sold in the European Union must meet the IE2 efficiency level.
From January 1st 2015, motors with a rated output of 7.5-375 kW must meet the IE3 efficiency level or meet the IE2 efficiency level and be equipped with a variable frequency drive. From January 1st 2017, motors with a rated output of 0.75-375 kW must meet the IE3 efficiency level or meet the IE2 efficiency level and be equipped with a variable frequency drive.
For circulators, the directive is founded on these assertions:
- The annual electricity consumption in the EU (EU27) is 1067 TWh per year
- The estimated electricity consumption in the EU without legislation would be 1252 TWh by 2020 – 20% of this amount is consumption from pump motors
- The estimated electricity consumption in the EU with legislation would be 1117 TWh by 2020.
This means that the directive implies electricity savings of 135 TWh within the EU by 2020 – or 5% of the EU’s total electricity use, which is similar to the residential electricity use of 83 million people in EU. This equals the estimated CO2 reductions of 54 million tonnes CO2 in the EU (EU27) by 2020
A non-return valve can be fitted to ensure that a medium flows through a pipe in the right direction, where pressure conditions may otherwise cause reversed flow. A non-return valve allows a medium to flow in only one direction. The flow through the non-return valve causes a relatively large pressure drop, which has to be taken into account when designing the system.
There are different types of non-return valves, such as spring-loaded, swing type, and clapper type valves. Non-return valves are e.g. used with mixing loops in heating and cooling systems to ensure proper operation, and with domestic water systems to prevent backflow.
A radial fan is a device that consists of an impeller driven by an electrical motor. The rotation of the impeller sets the air in motion and air is sucked in from the inlet on the side of the fan and blown out of the outlet of the fan. In a radial fan, the inlet hole is placed perpendicular (90º) to the outlet.
Radial fans are used in fan aggregates AHU and in connection with cooling towers.
The function of the recirculation pump is to ensure that hot water is always available as close to the consumption point as possible, in order to reduce water wastage and to increase comfort.
A recirculation pump can be sized for a given system using the following formulas:
Water flow qc= Φ/ΔT x 4200
qc = the circulating water flow [m3/s]
Φ = heat loss from the circulation system [kW]
ΔT = the water cooling, normally 5°C determined at the farthest consumption point [°C]
Normally uncontrolled pumps are used as the flow variation is relatively small. In large systems, however, it may be advantageous to use controlled pumps to enable adjustment of the flow when starting up the system and to be able to apply temperature control.
The International System of Units (abbreviated SI from the French Le Système International d’Unités) is the modern form of the metric system. It is the world’s most widely used system of measurement, both in everyday commerce and in science.
The six base units to provide for the measurement of temperature and optical radiation in addition to mechanical and electromagnetic quantities are: metre, kilogram, second, ampere, kelvin, mole, and candela.
Screw compressors are often used in connection with cooling systems. A screw compressor draws in coolant fumes continually, while some other compressor types draw in portions.
In a screw compressor, the compressor and motor are separated, and therefore connected with an axle or V-belt. As the compressor and motor are separated, the compressor can be used with ammonia as the coolant.
The cooling output of cooling systems can be regulated by adjusting compressor performance. A screw compressor is well-suited for regulation of cooling systems, as it features smooth adjustment from 100 % to almost 0 %.
The static pressure of a system is the pressure that is not provided by the circulator pump. In open systems, the static pressure depends on the geodetic height of the system. There are two types of systems: open systems and pressurised systems.
In open systems, the static pressure is defined as the difference in static pressure between the highest-placed open water level and the water outlet level.
A pressurised system typically has a pressure expansion tank, often with a rubber membrane, which separates the compressed gas and the water in the system.
The static pressure has a significant influence on pumps and valves. If the static pressure is too low, the risk of cavitation increases, especially at high temperatures.
The two most common installation types are free standing pump installation and pump installation on an auto coupling.
Submerged installation describes pumping equipment submerged in the wastewater in a wet well. The two most common installation types are free standing pump installation and pump installation on an auto coupling.
In this way the pump motor is cooled by the media in the sump. As a rule of thumb, the pump should not pump if the wastewater is below the middle of the motor part of the pump.
Suction lift refers to the pressure (negative pressure) on the suction side of the pump. The pressure can be measured from the centre line of the hydraulic part of the pump down to the water surface on the suction side of the pump.
In theory, it should be possible to suck water from a depth of 10.33 metres, however, this would require an absolute vacuum. In practice, the maximum is therefore much lower.
To avoid cavitations (the phenomenon of formation of vapour bubbles of a flowing liquid in a region, where the pressure of the liquid falls below its vapour pressure) it is important to compare the required NPSH (Net Positive Suction Head) to the available NPSH.
Tandem seal is Grundfos’ name for a shaft seal system, where an additional sealing chamber has been mounted on the existing shaft seal. The purpose of the sealing chamber is to guarantee that liquid does not leak from the pump housing. By flushing the sealing chamber with a neutral fluid, excess fluid in the centrifugal pump is absorbed/removed.
A Grundfos centrifugal pump with tandem seal offers several advantages. The flushing fluid between the two seals is pressure-less and gives several advantages to the product-side shaft seal such as:
- No evaporation in the sealing gap. This prevents the formation of deposits as well as crystallisation on the flushed fluid side.
- The flushed fluid lubricates and cools even when the pump runs dry or runs with vacuum.
TUV is an abbreviation for Technischer Überwachungsverein – a state-registered testing agency independent of manufacturers and operators.
Among other things, the agency conducts statutory testing and monitoring activities independently of manufacturers and operators. TÜV associations fall under the jurisdiction of the respective federal states.
The U-value describes the heat loss per sq. metre in relation to the temperature difference between the interior and exterior.
The U-value or transmission coefficient [W/m2K] is used in connection with the calculation of thermal energy. It is used when calculating the heat loss or gain within buildings and technical installations, as well as when calculating the dew point within a construction.
Heat loss per unit area
The U-value of a building element, insulation or other construction is the relationship between the heat flux density and difference between the temperatures of the interior and exterior of the construction. Therefore, the U-value describes heat loss per unit area in relation to the temperature difference of a construction.
A low U-value is indicative of a small amount of thermal energy transfer through the construction.
Water Flow Rate
Required heating capacity and required temperature differential of the medium are relevant when calculating the design water flow rate for a heating system. The following parameters are relevant when calculating the design water flow rate for a heating system:
- required heating capacity
- required temperature differential of the medium.