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New ! Cable Free Modbus Applications

Accountability Metering:

Accountability metering is a term used to describe the use of meters, sensors and software in commercial and industrial facilities to ensure that users are using energy efficiently. This process can be used to compare total usage for a number of different facilities or to measure energy usage within a single facility (a.k.a. behind-the-meter monitoring) or both. The purpose is to make users accountable for conforming to best practices in energy usage.

Tenant Sub-metering:

Tenant sub-metering is a broad term applied to the use of hardware and software to bill tenants in commercial facilities for their actual usage of energy. The goals of tenant sub-metering are: 
1) to ensure that the owner recovers the cost of energy from tenants, and 
2) to make sure that tenants with high energy usage are not subsidized by those with lower usage.


Measurement and Verification of Energy Retrofit Projects:

Scale Build-up & Corrosion

Water Level Control


Steam boilers and hot water boilers are usually subjected to diverse water treatment techniques.

Steam boilers are mainly provided with treatment which avoids build up of scale and corrosion. Scale build-up takes place inside a boiler due to the accumulation of dissolved minerals present in the boiler feed water. This boiler water loaded with minerals tends to replace the clean steam and condensate leaks. Strategies to prevent scale attempt to keep the components of scale such as calcium and magnesium suspended in the boiler water or to reduce their concentrations in the boiler water.

One of the common techniques used to trim down the concentration of solids inside a boiler is known as bottom blowdown. In this method, the water simply gets discharged from the bottom of the boiler. To avoid scale deposits, the sludge build up must also be frequently discharged from the boiler system. Now for eliminating corrosion, oxygen scavenging chemicals are generally mixed up into the boiler water. Finally, to reduce the possibility of scale build-up and corrosion inside a boiler, the regular checking of boiler water is required to be carried out.

The problem of scale build up is typically not encountered in hot water boilers. It doesn’t mean that the water fed inside a hydronic boiler is free of dissolved minerals. Actually the only difference is that the hydronic boiler systems are capable of discharging equal quantity of dissolved minerals as much is entering the system. Hence, the possibility of mineral accumulation inside the boiler gets totally eliminated. However, the hydronic boiler systems still face the problem of corrosion which can be solved via addition of oxygen scavenging chemicals only. 

Steam Boilers Vs Hydronic Boilers

A boiler may be defined just as a pressurized vessel in which heating of water takes place. It can be used for production of either hot water or steam. The operating principle of hot water boilers i.e. hydronic boilers and steam boilers is more or less same. However, there are few significant points of distinction lying in their equipment and processes which are mentioned in the section below.

In general, both hydronic boilers and steam boilers results in heating of water and generation of steam by burning of fuel. The heated water is then passed via boiler tubes while the steam generated is circulated in the building with the help of radiators. Though everything works in a similar fashion yet sometimes, the steam produced in steam boilers gets collected in a separate container. The burning fuel employed in a hydronic boiler is typically the same as used in steam boilers. However, owing to cost-effectiveness, use of natural gas is sometimes preferred in hot water boilers.

Steam boilers and hydronic boilers tend to find some differences in their application areas too. Since steam boilers are more robust, they are frequently put into use for industrial applications where hot water or steam is required whereas the use of hot water boilers is generally limited to domestic heating applications.

Water Tube Boilers

The design of Water Tube Boilers is strictly opposite to that of Fire Tube Boilers design. In water tube boiler systems, the water to be heated is enclosed inside the boiler tubes whereas the hot combustion gases exhausted by the burner keep circulating around the tube surfaces. The water within the tubes then gets heated via the hot flue gases and finally converted into steam. The diameter of the boiler tubes is kept very small in these boiler systems to provide them the capability to withstand higher pressures for the equivalent amount of stress. Water tube boiler designs are particularly suitable for high steam output requirements. Hence, their use is mainly preferred in industries for various types of process applications over home heating systems.


Operating Principle

Natural water circulation, also referred to as “thermo-siphoning” is the major working principle for almost all water-tube boilers. This principle is illustrated via the diagram shown below.

Cooler feedwater is introduced into the steam drum behind a baffle where, because the density of the cold water is greater, it descends in the 'downcomer' towards the lower or 'mud' drum, displacing the warmer water up into the front tubes. Due to continuous heating, steam bubbles gets created in the front side of boiler tubes. In the boiler drum, these bubbles get automatically separated from the heated water and finally carried out.

As soon as the pressure rises inside the boiler, the deviation between the water density and saturated steam density tends to reduce resulting in less circulation. To keep the same level of steam output at higher design pressures, the distance between the lower drum and the steam drum must be increased, or some means of forced circulation must be introduced.

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Fire Tube Boilers - Main Features

Key features of fire tube boiler systems include:

• Firetube boilers are often characterized by their number of passes, referring to the number of times the combustion (or flue) gases flow the length of the pressure vessel as they transfer heat to the water.
• Each pass enables the hot combustion gases to pass through the boiler tubes in the different direction. Every time, for conceiving next pass, the flue gases in the boiler make a shift of 180 degrees and go back via the shell.
• A typical three-pass boiler consists of three sets of boiler tubes whereas a four-pass boiler contains the four sets. The stack outlet in case of former one is normally positioned at the back end of the boiler while the latter one will have the stack outlet located at the front end.
• Various types of boiler tube arrangements are available for fire tube boiler systems depending upon the number of passes made by the hot flue gases emerging from the boiler furnace till the time they get cleared out of boiler system.
• In case of boilers made up of plain steel, the hot combustion gases going in to the reversal chamber are required to be cooled down to a temperature of 420°C prior to their entrance whereas in case boilers having alloy steel construction, this temperature should be at least 470°C. If the temperature of combustion gases happens to be more than recommended then problems like overheating and cracking of boiler tubes may take place.
• Since a fire tube boiler system consists of a considerable quantity of water within it maintained at saturation temperature point, it usually serves as significant energy storage ground to deal with very quick short term load applications. However, this fact can pose a major limitation also since re-buildup of energy reserve would be required which may consume large time.
• Nowadays, the largest shell boilers offering 1,500 boiler horsepower i.e. approximately 50,000 lbs/hr have been made available.

Types of Hot Water Boiler Systems

How It Works

Types of Hot Water Boiler Systems

There are four major types of hot water boiler systems available which are mentioned below:

1. Closed System: In these types of systems, the water which gets evaporated and converted into steam is again put back into use by condensing the steam back to liquid form. This means that the 100 percent reutilization of the water takes place in closed systems.
2. Open System: In these systems, the water is heated up but the evaporated water is not put back for reutilization inside the system.
3. Single-pipe System: In these systems, two pipes are utilized. One pipe is used for carrying the heated water to the required location whereas the second pipe is used for returning the cool water back towards the boiler by means of a motorized pump.
4. Gravity System: These are the older hot water boiling systems in which the water is carried back after heating via the gravity effect. Hence, in these systems, circulators are not required.

Main Features

Following are the significant features associated with the use of hot water boiler systems:

• Although the installation of hot water boiler systems is extremely costly yet they are frequently employed for heating applications owing to their high efficiency and cost in comparison to forced-air boiler systems.
• Since the hot water boiler systems are made up of aluminum fins and copper pipes, they tend to employ less metal for their construction and hence occupy comparatively smaller area.
• Hydronic boilers typically offer small and uniform values of temperature as compared to forced-air boilers. Moreover, in these systems, the on-off switching action is usually prevented because of the ability of baseboard pipes to grasp the heat and liberate it over longer periods of time.
• Another important feature regarding hot water boilers is that they dry the air inside the system to a very small extent only.
• A Hydronic boiler does not allot allergens, dust, combustions or mold by any products that enter living space. This is always an advantage, especially for a family that is sensitive with allergies.
• The piping mechanism within a hot water boiler system is very exceptional and its correct implementation is very much responsible for the proper operation of the boiler.
• A single hydronic boiler system per home is usually found adequate to produce necessary heating effect, unless it’s a big triple story house.
• Hot water boilers are mainly employed for domestic heating applications, generally in the northern parts of Europe.
• Hydronic boiler systems are mainly applied as central heating system inside buildings to give heating effect to the areas, which are otherwise very cold.
• A typical hot water boiler operates throughout the winter with a water temperature determined by the Aquastat, or low limit, setting (an Aquastat is like a thermostat that senses the water temperature inside the boiler and shuts off the burner when the water is hot enough).

Steam Boilers Safety Control

A steam boiler is capable of generating superheated steam having temperature more than 212 degrees F. However, this temperature can go beyond unsafe limits and result in fire breakout, if adequate safety controls are not incorporated within the boiler system. Hence, for safe and sound operation of steam boilers, following safety controls must always be provided:

• Limit switches: These are the safety switches which are basically included in the system to detect the increase of temperature beyond a certain limit. As soon as the temperature inside the boiler crosses the defined limits, a limit switch operates resulting in the shut down of the whole system. It is usually mounted near the draft diverters. It proves to be a useful device in preventing fire breakouts and plugging up of chimney or flue gases. It helps in avoiding carbon monoxide poisoning or any other dangerous situation related to temperature rise.
• Low water cut-off: This safety feature should always be incorporated in the boiler system for keeping a check on the level of water in the boiler. The normal level of water is in the half-way in the gauge/ sight glass which should always be maintained. For carrying out a regular visual inspection of water level, the sight glass indicating the level must be kept clean and free from dirt. Lower than average water level in the boiler may lead to undesirable results.
• Automatic water feeder: This device is generally employed for automatically feeding water into the boiler system whenever the water level drops below a certain point. Appropriate water level will result in generation of high quality steam heat. However, small adjustments are needed in the system to maintain correct water level i.e. neither too much high nor too much low. Since excess water will not heat up the system whereas scarcity of water may cause hazardous situation.
• Pressure cut-off control: Various devices such as pressure relief valves and blow-down valves etc. are employed in the boiler system for exercising control over excess steam pressures. 

 Type of Steam Boilers

Demand Load Management

Within a boiler system, the operating steam pressure and hot water temperature must always be maintained at a constant level regardless of the load demand placed on the system. “In a multi-boiler plant, demand-load management optimizes the distribution of steam demand among the units and adjusts the overall output to meet working requirements.

By adopting a proper demand load scheduling technique, one can easily cut down the running cost of the boiler plant since via this technique, firing of boilers take place only in case of actual need. On the other hand, demand-load scheduling can be used to run each boiler for exactly equal periods of time.


Main Features

Major features of demand-load management in boiler systems are listed below:

1. Base load or modulating operation
2. Parallel or serial demand sharing
3. Boiler banking operation and programmable sequence selection 

Features

Boiler Water Source

Both hydronic boilers as well as steam boilers require a water source for their operation. This boiler feed water can be obtained either in the form of city water supply or well water that is provided by the pump. Barring any leaks, drips, or weeping in your system, the supply from the well or city is necessary to keep the water level at desired levels.

A boiler fired in its dry state may lead to hazardous results. Hence, it is very crucial to maintain appropriate water levels in a boiler system. In case of hydronic boilers, the system must be entirely filled with water whereas in steam boilers, the level of water should not touch the mains otherwise the system will not work properly. In steam boilers, a control at the water supply must always be maintained to limit the water levels.

A gate or ball valve is usually employed to stop the supply of water in periods of maintenance or water leaks. When the water supply is put to a halt, the power and fuel source supply should also be cut from the boiler system. After the shut off valve there should be a back flow preventer, however there may be some older systems that do not have back flow preventer's. Current local and national codes require back flow preventer's to keep the supply water from being contaminated by back flow water from the hot water loop. Subsequent to the back flow preventer, a pressure reduction valve should always be mounted for the purpose of bringing down the supply water pressure upto 12 P.S.I. After the pressure reducer, the source supply water should be fed into the return or supply loop depending on the application and type of system.

Commonly Used Fuels II

Commonly Used Fuels

 

Oil

With the advent of fuel oil, solid fuels such as coal and wood increasingly got replaced in nearly all parts of the world owing to its cleaner and ash free combustion process. Oil fuels generally consist of less carbon content as compared to solid fuels such as coal, which in turn results in less emission of carbon dioxide upon combustion. On the other hand, oils contain higher carbon content as compared to natural gas producing high amounts of carbon dioxide due to burning.

The fuel oil employed for boiler use is mainly manufactured from a mix of extremely heavy hydrocarbons, which tend to contain relatively high amounts of hydrogen content in comparison to coal. Burning of a fuel oil usually produces same kind of pollutants as produced with burning coal. Heating oil is a boiler fuel which is widely employed in the northeastern areas of the United States whereas in other parts of the world, it is facing severe competition with the gaseous boiler fuels available.

Diversity of oil fuels is available for heating such as oil #2, oil # 4, and oil # 6. Fuel oil #2 is popularly referred to as the home heating fuel. It is almost identical to the diesel oil fuel which is largely employed in vehicles and automobiles. Its energy value is found to be approximately 139 kBTU per gallon.

Boiler and heating systems that employ oil for its operation happen to be more expensive than gas powered boiler systems since they need complicated burner mechanism as compared to their gas counterparts for efficient firing. However, at the same time, this difficulty of ignition (or firing) in case of heating fuel turns out to be a great plus point since it results in safer storage of fuel oil in comparison to gas. Otherwise, a leakage in the fuel tank could prove to be very costly and hazardous.

Natural Gas

Natural gas is the key fuel source for boilers which is widely employed in United States and Europe for home heating needs. It is largely prepared from methane along with a mixture of few other gases in small proportions. Natural gas has an energy content of about 100kBTU per therm or 103kBTU per ccf (100 cubic feet). However, anecdotal evidence suggests that the actual heating value of "Natural Gas" coming out of the distribution pipe may vary from as little as 60kBTU up to 160kBTU per ccf.

Natural gas can be conveniently put into use for boiler applications since it can be transported easily via gas pipelines when in gaseous sate and trucks or ships when in liquid state. Very less amount of air is needed for burning of natural gas owing to its unique C/H2 ratio. This fuel contains quite low values of carbon and high values of hydrogen because of which the combustion of natural gas results in production of less greenhouse gases which are considered to be highly responsible for global warming. Also, the burning of natural gas is found to be very clean as compared to the burning of oil and solid fuels oil.

In general, an equivalent amount of natural gas burns to generate approximately 30% and 45% less carbon dioxide than heating oil and coal respectively. Besides, carbon dioxide gas, burning of natural gas emits an ingredient called NOx whereas the quantity of sulfur dioxide i.e. SO2 and other emission particles is almost insignificant. However, if the burning of gas takes place facing scarcity of combustion air, there is a possibility of volatile hydrocarbons generation which is very unsafe to human health and surroundings. Hence, care must be exercised to avoid these hazardous possibilities.

Nowadays, natural gas fuel reserves are getting exhausted at a rapid rate. Hence, substitutes for this boiler fuel need to be discovered very soon.

Factors Affecting Boiler Efficiency

Some of the important boiler-efficiency deciding factors are explained in brief below:

Stack Temperature

It is also referred to as flue gas temperature. It is defined as the temperature level at which the hot exhaust gases make their way out of the boiler. The flue gas temperature must be a proven value for the efficiency calculation to be reflective of the true fuel usage of the boiler. Lower than real stack temperature values must always be used for boiler efficiency calculations.

Fuel Specification

The specification of a fuel source can immensely affect the efficiency of a boiler system. For example, if the hydrogen content within a gaseous fuel source is comparatively high, extra water vapors get generated in the burning process. These water vapors tend to consume heat energy from the boiler for shifting their physical state during combustion. The efficiency of the boiler generally drops if huge loss of water vapors takes place. Due to this, the fuel oil offers greater boiler efficiency as compared to natural gas. To get an accurate efficiency calculation, a fuel specification that represents the jobsite fuel to be fired must be used.

Excess Air

Excess air is defined as the amount of surplus air provided to the burner which is more than the necessary air needed to carry out combustion process. This given excess air mainly acts as a safety air reservoir for combustion in difficult situations such as inadequate air conditions.

However, at the same time, this more than required air tends to consume heat energy produced by combustion which in turn affects the heating efficiency of the boiler. Seasonal changes in temperature and barometric pressure can cause the excess air in a boiler to fluctuate 5% - 10%. A realistic excess air level for a boiler in operation is 15% if an appropriate safety factor is to be maintained.

Ambient Temperature

The efficiency of a boiler also depends upon the ambient air temperature surrounding the boiler. For every 40 degree shift in ambient temperature, the efficiency of a boiler can get affected by at least 1%. Since all the boiler rooms are maintained at moderately warm temperature, majority of the efficiency computations takes upon 80 deg. F as the ambient temperature value.

Radiation & Convection Losses

These are the losses which emerge due to radiation of heat energy from the boiler. To eliminate the effect of these losses, boiler systems are usually shielded with some sort of insulation material. The presence of these losses extremely influences the efficiency of a boiler. In cases where these losses are not taken into consideration while performing efficiency calculations, accurate fuel consumption value can never be attained.

A boiler must always be designed in such a way that the radiation and convection losses get minimized. These losses tend to increase in proportion to the wind or air velocity prevailing around the boiler. Hence, the boiler systems located in open atmosphere experience more radiation and convection losses as compared to room boilers.