Programming of the abandonment of gas R22 refrigerant:

From 01/01/2010:

• It is not longer possible to produce and export machines with R-22 (for the European market the ban dates back to 2001)
• It is no longer possible to use the gas R-22 “virgin” for top-up or replacement during maintenance operations.
Replace your old refrigerator R22 and save 25%
A modern chiller with scroll compressor and R410A gas consumes 25% less than an old R22 chiller with reciprocating compressors.

Let’s take an example of how much you can save by replacing an old refrigerator power rating 70,000 kcal/h, assuming an age of 10 years, a natural drop in performance over time of evaporator and condenser, R22 and reciprocating compressors.

Old refrigerator consumption: 172,763 kWh / year
Coefficient of refrigeration old refrigerator consumption: 4,13
Last generation Tempco refrigerator consumption: 128.631 kWh/year
Coefficient of last generation Tempco refrigeration: 5,52
Saving 25%
= 44.132 kWh/year at medium cost of 0,15 Euro/kWh
= 6.619,00 Euro/year
If the same is associated with a free cooling system, the savings can exceed to 80%.

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Reciprocating engines energy coming from fuel is converted to:
• 30-40% mechanical power
• 20-40% rejected to the jacket water
• 30-40% rejected to exhaust
• 5-7% radiated to the environment
these data depends from kind of engine and manufacturer.

The heat rejected by the jacket water can be totally recovered.
The 50-70% of the exhaust rejected energy, in economically recoverable, more then this value is not achievable, due to problem of low temperature of exhaust and corrosion resistance of heat exchangers.

Total heat recovery results in approximately 75-80% efficiency.
Heat recovery design best suited for any installation depends on many considerations, both technical and economic.
We need to keep in mind that the primary function of any design is to cool the engine. The engine must be cooled even when heat demand is low, but power is still required.

Usually energy is recovered producing hot water or superheated water, sometimes producing steam.
To achieve recovery on engine the best solutions are:
• Plate heat exchangers for water jacket recovery
• Special shell and tube heat exchangers for exhaust recovery.

Heat Balance
The typical heat balance for an engine is shown in the figure below.

L'articolo Heat Recovery on engine proviene da Tempco Blog.

The heat exchanger is a device which is needed to transfer thermal energy (heat) between two liquids with different temperatures

There are many types of heat exchangers which vary depending on the different type of liquid used to transmit and exchange heat.
Heat exchangers are “passive” devices that do not generate heat. They simply transfer it.
There are mixing and surface heat exchangers: quite a few of the latter type are on the market and are classified depending on the building type.

The different heat exchanger types, based on construction technology, are:

• (shell and tube) heat exchanger: one of the liquids goes through the circular section tubes and the other one circulates on the outside of these same tubes which have deflectors (septa) that increase their turbulence (i.e. the heat exchange);
• (plate heat exchangers): the two liquids lap the opposite sides of flat or corrugated stainless steel by inserting turbulators in alternating areas. They are isolated from each other by seals and and weldings (inspected or welded), usually in counterflow motion;
• spiral heat exchangers: the two fluids pass on the opposite sides of a smooth plate wound in a spiral casing;
• heat exchanger blocks: the liquids circulate in cylindrical (or oval) holes, usually placed at right angles on the two sides (typical construction in graphite);
• finned, battery or radiator heat exchangers: one of the fluids goes through the inside of the tubes and the other (gas-type) goes through the finned pack on the outside of the tubes.

L'articolo Heat exchangers proviene da Tempco Blog.

Storage tanks also function as “expansion vessels”. The expansion tank has a dual function: thermal and hydraulic.

From a thermal point of view its function is to allow water, which is an incompressible fluid, to expand or contract. In order for this to be possible it is necessary for the fluid to be in contact with a gas that can compensate for the expansions and contractions of the fluid.

There are three possible configurations:

• open atmosphere vessel;
• closed vessel, containing water and air (or other inert gas) without any for of separation (self-pressurization or pressurization with air or gas that is inserted from the outside);
• closed vessel with a separating membrane between the water and an inert gas (nitrogen)

The volume of the expansion vessels can be calculated by using the following expressions:

for a vessel that is open to the atmosphere:

for a closed vessel without a diaphragm:

for a closed vessel with diaphragm:

where:
V_v = the volume of the expansion vessel (L)
V_w = the volume of the inside the plant (L)
v₁ = the specific volume of the cold water at a lowest temperature t₁ (m³ / kg)
v₂ = the specific volume of the water at the highest temperature t₂ (m₃ / kg)
α = the coefficient of the expansion of metals (see table)
– per steel α = 1,2 . 10^-5 (1/K)
– per copper α = 1,65  10^-5 (1/K)

∆_t = t₂ – t₁ (°C)
P_a = absolute atmospheric pressure (bar)
P_i = initial absolute pressure at the lowest temperature t₁ (bar)
P_f = absolute pressure while functioning at the highest temperature t₂ (bar)

The expression:
V_w [(v₂/v₁) – 1] – 3 α∆t (L)
represents the volume variation.

In hot water systems the reference temperatures are predominantly:
t₁ = the temperature during filling, 10 °C
t₂ = the water’s maximum flow temperature 85 : 90 °C

In superheated water systems the temperature t₂ can reach ​​up to 130 ° C and beyond.
Instead in cooling water circuits:
t₁ = the maximum water temperature that can be reached when the system is not functioning, 35°C;
t₂ = the minimum functioning temperature, 7°C, for example.

The water’s specific volumes are shown in the following table.

From a hydraulic point of view the expansion tank determines and sets the system’s pressure reference. At the point in which the vessel is inserted in the circuit, the pressure is equal to the vessel’s air pressure which is increased or decreased by the liquid located above or below.

Pressure values at the insertion point of different types of expansion vessels.

Open expansion vessel
As can be see by its expression, the vessel’s capacity must be at least twice the water’s expansion volume in order to prevent water from leaking due to possible overflow during the heating phase and is fed back into the vessel again during the cooling phase. The illustration shows the accessories that the vessel must be equipped with.

Open expansion vessel

The vessel and the safety tubes must be protected from freezing temperatures. As far as systems using many boilers is concerned it is good practice to provide each with its own boiler expansion vessel, thus making it possible to eliminate one or more boilers.

Expansion vessels for three specific generators.

The hot water heating systems that use open expansion vessels, with a functioning pressure that does not exceed 5 bar, should be provided with:
– a safety pipe between the vessel and the generator that has a diameter equal to its virtual length and to the generator’s thermal power (see; “Safety standards for appliances containing hot liquids under pressure”);
– automatic adjusting thermal switch;
– automatic blocking thermal switch;
– a thermometer with an inlay for the checking thermometer
– a pressure gauge with flange for the checking pressure gauge.

The illustrations below show some possible connection diagrams; the illustration of the connection of the expansion tank with filler and safety pipes is typically used in the German DIN standard and the diameters of the tubes, as a result of this standard, can be calculated by using the following expressions:
– in the event of overheating, the safety pipe must be able to vent any vapor produced in the boiler.

– for the expansion or loading pipe which must enable the speedy filling of the boiler using water from the vessel.

– where P is the power of the generator or generators expressed in kW.

Connecting the open expansion vessel to a boiler.

Connecting the expansion vessel with loading and safety tubes.

Should there be many heat generators which run the same plant, a safety pipe that is sized for the nominal capacity of all the generators can be used; only the connections of each generator to the normal safety tube can be sized for the single power. Should it be necessary to separate the generators from the expansion vessel, the pipes that connect each generator to the safety pipes must be installed with three-way valves using a passage cross section that is not smaller than the valves on the generator’s security tube. This ensures the connection between the generator and the atmosphere either via the safety pipe or via the vent tube.

Connecting two heating generators to only one safety tube.

The vent tube must be conveyed in order to prevent it from causing to persons in case there is water discharge. Systems with a functioning pressure exceeding 5 bar must have a secondary automatic blocking thermal switch independent from the other switch. As far as the position of the circulation pump is concerned, with respect to the vessel’s circuit connection point, we should pay close attention because the circulation pumps must be installed in the water distribution network in a way that both physical and technical functions can be carried out. It should be noted, above all, that tube throttling should not be carried out on the open vessel plant’s two safety pipes: therefore, a pump, whatever type it may be, is considered a choking device and must consequently be installed in areas away from the connections with the vessel. Another important aspect that should be taken into consideration is installing the pump with respect to the boiler: suction (when sending) or under pressure (when returning).

There are no safety requirements regarding this issue: the problem is solved by taking into consideration that no point in the network should be in depression. The piping networks, in fact, are never perfectly sealed against air, which can penetrate, for example, if a heating body goes into depression, through the control valve’s stuffing box. In order to verify the pressure of the piping network’s critical points it is necessary to check the diagram of the pressures along the circuit and to check the installation instructions. Let’s look at the following two examples of a start pump and a return pump.

Start pump. Installation instructions and pressure diagram.

Return pump. Installation instructions and pressure diagram.

The _AH static pressure prevails on the starting pump at point A, where the expansion vessel is connected. At the pump’s exit the pressure value increases in proportion to the pump’s manometric height, then as the water flows in the circuit, the pressure decreases to the pump’s suction value. Items 1.2.3.4.5.1. are a graphical representation of the pressure variations along the circuit. Point 4 represents the pressure in radiator M. When the water circulates, the pressure is positive; however if the valve is closed the pressure in the radiator is the same as the return pressure, represented by point 5, whose ordinate is, however greater by Δ than the static pressure H_A, defined uniquely by the water level in the expansion vessel. At point 5, pressure H_A + ∆ prevails.

A closer look at the problem shows how the lowest radiator is not at risk. The highest one is in danger because the pressure is less than HN compared to the lower radiator. This pressure’s value is:

H_A + Δ – H_N = (H_A – H_N) + Δ

The term (H_A – H_N) is the difference between the vessel’s water height and the radiator N height. In this scenario too the pressure is positive.

Let’s now examine the return pump.
The line that goes from here too represents the pressure flow between the radiator M and the pump, however it is placed below the line of the static pressure between the radiator M and the pump. We can also note that it is placed below the line of the static pressure of a value equal to the height of the manometric pump.
The pressure in 5 is worth H_A – H_P + Δ. The pressure in the radiator at risk, or let’s say the highest radiator, is:

H_A – H_P + Δ – H_N = (H_A – H_N) – H_P + Δ

In order to avoid this value from becoming negative (depression in the highest radiator) it is necessary (let’s neglect Δ to be on the safe side) for H_A – H_N , or rather the level difference between the vessel and the highest radiator, to be greater than the pump’s prevalence.  In some buildings where H_A – H_N is 3 : 5m it is quite probable to see a pump, which has slightly less prevalence, ensure the circuit’s water circulation without any form of depression.
It is therefore necessary to evaluate each scenario and to appropriately position the pump’s flow, whether it be start or return flow. The start pump ensures that no point of the network goes into depression. The possible disadvantages are that water at high temperatures could get into the pump and as a result there could be high pressure in the network.
The illustration below gives details of the equipment required by IPESL regulations for an open vessel system.

Security equipment required by ISPESL regulations – open vessel.

Closed expansion vessel
We have already seen at the beginning of the chapter how to calculate the capacity of a closed vessel, in the expression which is valid for a closed vessel without the diaphragm, the absolute pressures to consider are:
P_i = absolute initial pressure corresponding to the hydrostatic pressure at the point where the vessel is installed measured in bar (kg/cm²), increased by an amount determined by the designer and, however, not less than 0.15 bar;
P_f = maximum absolute functioning pressure, in bar, equal to the calibration pressure of the safety valve, increased by the excess pressure of the valve and decreased by an amount corresponding to the difference in height between the expansion vessel and that safety valve, if the latter is placed lower or in other words increased if placed higher.

A closed vessel system without a diaphragm.

For closed vessels with a diaphragm, assuming the definition is P_f, the P_i pressure to place in the the closed vessel with a diaphragm is:
P_i = absolute pressure in bar to which the gas cushion is precarious, a pressure which cannot be less than the hydrostatic pressure at the point where the vessel is connected.

Closed vessel system with diaphragm.

The expression of vessels without a diaphragm can only be applied to self-pressurized vessels where the pressure prior to filling is equal to the atmospheric pressure. For pressurized vessels, for example where the pressure before filling is greater than the atmospheric pressure, and has a variable pressure while functioning, the formula to be used for testing is the same used for the closed vessel with a diaphragm, and even for vessels without a diaphragm, increasing the volume resulting from the calculation of a quantity equal to the initial volume of water contained in the cold system vessel; in which case the system designer must indicate, in addition to the pre-charge pressure and the total vessel volume, the volume occupied by the gas when the system is cold.

For pre-pressurized vessels at constant pressure and variable pressure level during functioning, the tank volume must be calculated the same as for open vessels. For pre-pressurized vessels that have a constant level and pressure while functioning, the volume of the vessel must be sufficient enough to contain the excursions necessary for the devices needed when discharging and water re-integrating is necessary.

In closed vessel heating systems with a power up to 350 kW and a working pressure that doesn’t exceed 5 bar, you must have:
– a safety valve which enables the discharge of a quantity of steam per hour (kg/h) of not less than P/0.58 (where P is the power of the generator in kW);
– automatic thermal regulating switch;
– automatic thermal blocking switch;
– blocking control device;
– thermometer with small well for the checking thermometer;
– a pressure gauge with flange for the checking pressure gauge.

Even with closed expansion vessels it is possible to exclude heat generators provided that the pipe connected to the vessel’s generator is installed using a three-way valve with the same open vessel characteristics. It must ensure the generator’s connection either with the expansion vessel or with the atmosphere. With closed vessel, circulation pump heating systems the heat input must be automatically interrupted should the pump stop functioning and this can be implemented with an electric burning pump or via a flow switch.

Closed vessel pressurized systems that run on constant pressure and at a variable level must be protected by a fuel shut-off valve or a temperature relief valve because there is no correlation between increased temperature and pressure. For systems with a pressure exceeding 5 bar a second blocking thermostat must be installed which is independent from the first one.
The illustration below shows the instrumentation required for closed vessel systems.

In addition to what has already been written please note:
– automatic filling unit which reduces the aqueduct’s supply pressure and reintegrates any losses of water in the cold state; the filling unit is made up of the pressure reducing valve, the filling valve and the restraint and filter valve.
– air separator with automatic vent valve and float.

Safety and control instrumentation for a heating system with a closed vessel (the symbols used are those used by the regulating standards).

• 1 burner
• 2 boiler
• 3 safety valve
• 4 fuel shut off valve;
• 5 expansion vessel with membrane;
• 6 automatic regulating thermal switch;
• 7 automatic blocking switch;
• 8 pressure control device;
• 9 pressure indicator;
• 10 temperature indicator;
• 11 little well;
• 12 accessible and visible discharge;
• 13 circuit pump;
• 14 pressure reducer;
• 15 non-return valve;

16 water counter (possible) .

L'articolo The expansion vessel proviene da Tempco Blog.

The evaporative cooler is a very simple device, which serves to cool water by direct exchange with air.

There are different types of evaporative towers:

• induced, with suction fans
• forced, using forced ventilation
• counter flow, with countercurrent water and air flow
• cross flow, that uses a crossing flow of water and air

in any case all of these machines work using the same concept.

The counter-flow type is the most widely used, whether it be forced or induced, because it presents greater functioning efficiency.

EVAPORATION…EVAPORATIVE, why?

Compared to a conventional radiator it is more efficient because the evaporation effect of the water is exploited as a result of the direct exchange, thereby taking advantage of the latent heat evaporation.

The reference parameter therefore isn’t the ambient temperature, it is the temperature of the moist bulb, or rather the temperature that we can determine using the psychrometric chart, based on ambient temperature and relative humidity.

The tower’s ambient temperature is usually 4 ° C to 6 ° C (or even higher​) less than the ambient temperature. As a result the cooling tower is able to cool the water at a temperature below ambient temperature.

Furthermore, by exploiting the latent heat evaporation efficiency is considerably increased. In fact, on average for every kilogram of evaporated water there is a dispersion of 600 kcal/h (average value). This fact implies that a cooling tower, by its very nature, consumes water, therefore we cannot consider the cooling tower circuit as a closed circuit. In fact there is a constant consumption of water, which is linked to the potential dissipation.

WATER CONSUMPTION

The following formula enables us to evaluate the average water consumption of an evaporative tower:

Qc = P / 600

where:

• Qc is the amount of water used expressed in Kg/h
• P is the tower’s thermal power expressed in Kcal/h
• 600 is the amount of heat extracted from each kilo of evaporated water (KCal / Kg) on average…the correct value should be taken from the steam diagram based on actual operating conditions. On the first approximation however, this value is rather accurate, as we will see in the explanation below.

The result of this simple formula gives us the value of only the water that is consumed by evaporation.

We must add to this value:

• the amount of water loss due to drag
• the amount of wastewater purge

The losses due to drag, using current drift eliminators, are almost irrelevant. The amounts in question are losses of roughly 0.1 to .05% of the total value of the recirculating flow.

The amount of wastewater purge however depends on several factors:

• the quality of the water that is re-integrated
• the type of conditioning applied to the water
• concentration cycles

Essentially these three parameters are closely linked to each other and depend mainly on the quality of the water that is re-integrated.

In any case due to the continuous evaporation of water, a gradual concentration phenomenon takes place, which will change clean water to a state that is unacceptable for cooling circuits. This phenomenon forces you to re-integrate, clean and condition the water.

Rather than going into a detailed discussion of these aspects we can say that at a first approximation, particularly if we’re making some considerations regarding the consumption of water by a cooling tower, we can assume that the flow of the wastewater purge is equal to the water lost due to evaporation. In brief we can say that the average consumption of water in an evaporative tower is the result of the sum of water losses due to drag in addition to double the evaporation losses.

WATER CONDITIONING ACCESSORIES

Proper and careful management of the cooling plant, along with a valid water conditioning system, will eventually optimize the consumption.

To complete the picture of this brief analysis, we can say that a water conditioning system of an evaporative tower must have:

• an anti-scaling dispersion product with relative dosage pump
• an algaecide product with relevant dosage pump
• an automatic purge valve
• a conductivity meter with relevant probe
• a litre counter
• a control unit

L'articolo How does a cooling tower work and how much water does it use? proviene da Tempco Blog.

The calculation of a heat exchanger, is all in all a fairly simple exercise. It involves applying a mathematical formula using a set of pre-established data and coefficients.

Obviously this is assuming we limit ourselves to the calculation of the exchange surface which is required for a certain type of thermal work.

A series of factors come into place to establish the actual size of a heat exchanger

• construction type
• limited project conditions
• internal heat flow
• turbulence
• etc…

These factors determine the actual size of the exchanger and as a result they become the essence of the project.

It is not my intention here to dwell upon complex issues but I do wish to summarize some fundamental concepts regarding heat and its transmission to the basic dimensions of a heat exchanger.

The following are some excerpts from the document that can be easily downloaded.

HEAT TRANSMISSION

IN GENERAL

When there are two bodies at different temperatures the temperature of the warmer body diminishes while the temperature of the colder bodies increases. The progressive reduction of the difference in temperature must be transferred to an energy exchanger. The exchange must continue so long as there is a difference in temperature, in other words until the thermal equilibrium is reached. When the transfer of energy takes place as a result of a difference in temperature and no work is carried out on the substance, it is considered a science that is called heat transmission. The transmission of heat is essentially energy that is transmitted as a result of a difference (gradient) of temperature ∆T. This energy transfer is expressed as the amount of heat q transmitted in the unit of time t; it is a flow of heat which is named the thermal flow Q = q / t and is measured in W, since 1 J/s is equivalent to 1 W, Q is therefore the heat power. The energy transfer is carried out in three ways:
• conduction: when the transfer of heat, which is produced by the temperature gradient, takes place in a solid body or in a fluid at rest;
• convection: on the other hand is the heat transfer that takes place between a surface and a fluid in motion with different temperatures;
• irradiation: all surfaces that are at a given temperature emit energy in the form of electromagnetic waves. Therefore, in the absence of a medium located between them, the heat between the two surfaces at different temperatures is transferred only via irradiation.
These forms of transmission almost always coexist.

QUANTITY OF HEAT

The amount of heat, contained in a liquid gas, or in a body, is usually:

q = cp• m •∆T

where:

• q= the amount of heat, in J
• cp= the heat capacity mass at constant pressure, in J/(kg •K)
• m= the body mass, in kg∆T= the difference in temperature, in K

…………………………………………………….

EXCHANGER PROJECT

In order to design a heat exchanger we must correlate the amount of heat transmitted per unit of time Q with the input and output temperatures of the two fluids of area A of the total surface required for the given heat exchange.

Using the energy balance equation of hot fluid open systems (subscript c) and cold fluid open systems (subscript f), characterized by the mass flow rate mc and mf, you obtain the following two expressions.
The energy balance equation, written in terms of heat flow and through the output enthalpies (subscript 2) and input enthalpies (subscript 1), of the two fluids is:
Q = m ( h2 – h1)
Keeping in mind that, a perfect gas enthalpy expressed as a function of the temperature is:
h = c p • T

we have a first equation relating to the cold fluid, ie the flow Q that enters the cold fluid, thus increasing the temperature, is:
Q = mf • c pf • ( t f2 – t f1) (1)
c pf being the thermal capacity mass of the cold fluid.
Removing the heat flow Q however, decreases the temperature of the hot fluid from the input value t c1 to the output value tc 2, the equation for the heat flow is therefore:
Q = mc • c pc• ( t c1 – t c 2)
c pc being the thermal capacity mass of the hot fluid.
Once the thermal gradient is known, or calculated based the above-mentioned balance equations, we proceed to the sizing of the area A of the exchange surface, using an equation which links the heat transmitted in the unit of time Q between the two
fluids with area A and the average difference in temperature ΔTm of the two fluids.

Q =U ·A ·ΔTm
The link between the thermal flow Q and the product of area A for the average difference in temperature is expressed by the overall coefficient of exchange U, which is determined empirically.

Heat exchanger calculation

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