In a centrifugal pump, Why is the suction line diameter usually larger than the discharge line diameter?

1. To Reduce Friction Losses in Suction

a.  A larger suction pipe means slower fluid velocity.

Lower velocity = less friction loss in the pipe.

b. This helps maintain higher pressure at the pump suction.

Less friction = higher NPSHa (Net Positive Suction Head Available), which helps prevent cavitation.

2. To Maintain NPSHa Above NPSHr

a. Cavitation occurs if pressure at the suction drops below vapor pressure.

b. A large diameter reduces pressure drop, helping to keep suction pressure above vapor pressure.

c. This is especially critical in high-flow or hot fluid systems.

3. Discharge Side Can Handle Higher Pressure

a. On the discharge side, the fluid is already pressurized by the pump.

b. Higher pressure = smaller pipe can be used, and the fluid can still flow efficiently.

c. Slightly higher velocity on discharge is acceptable (and sometimes even desirable)

Isometric drawings of pipes

Isometric piping diagrams are isometric representation of a single pipeline in the factory. It's the most important output of pipeline engineering department. Pipe manufacturing work depends on isometric drawings.

The isometric diagram of pipes consists of three sections. The main section consists of isometric representation of the pipeline path in 3D space, and includes the following information:

1. The line number.

2. The direction of the flow

3. Poster signs and props.

4. Site of pipe components.

5. Welding sites.

The section to the left or right of the drawing includes a material list section for the portion of the line that appears in the isometric drawing. This section includes the following information for all components:

1. Describing the ingredients.

2. The ingredient code.

3. Nominal size.

4. Quantity.

5. Whether material for manufacturing shop or field work.

6. The number of pieces.

The title bar section at the bottom includes the following information:

1. Project details such as client name, engineering office name, project name, project number, project processor license, etc.

2. Pipeline details such as line number, line size, isolation, tracing, liquid code, operating and design pressure and temperature, pressure testing method such as hydraulic or aeronautical test, test pressure, pipe material category, inch diameter, etc.

Accounts:

Inch Meter = Length of pipes in meter x Size of pipes in inch

Inch Dia = size of pipes in inch x number of connections

Isometric Diagram Checklist:

The isometric diagram should be checked according to the project's isometric diagram checklist. This list includes general points as well as project-specific points.

Symbols of Isometric Graphics

Description: Link of codes

Project-specific instructions for testing isometers: Each project has its own requirements. These requirements should be reflected in isometric diagrams. Some of these requirements may relate to:

1. Pressure Safety Valves

Screw Supply Range (Input/Output)

Bolts and bolts in the line, inlet or exit.

2. Fire fighting lines

Pipe cutting requirements.

Types of edges (flat edge or high edge).

3. Ventilation and practical drainage

Ventilation and drainage requirements for hydraulic testing.

Direct distance requirements for flow meters.

4. Insulation of pipes

Isolation fish and its range.

5. Selection of valves / alignment

6. Requirements of jack score rim.

7. Identification of the Pros.

8. The requirements of connections / lovers.

9. Dimensions of galvanized pipe cutting.

10. Signs of the rooster crowing.

11. Notes of mounting props.

12. Channeling the rim of the Orivice.

13. Sequence of delivery in PID layout

14. Edges/fills and bolts at the end of iso sheet.

15. Philosophy of disconnection of paper.

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The professional post:

🔧 Everything you need to know about pipe isometric drawings! 🛠️

Isometric drawings are an essential component in the design and execution of piping in industrial projects. In these graphs, you can find everything about the pipeline, from line number to welding locations and props. These drawings are the document on which the piping department relies on to carry out the work accurately and professionally.

💡 What the isometric diagrams include:

1. Basic information such as line number, flow direction, and pipe supports.

2. Detailed information such as details of materials, sizes and quantities.

3. Tests and methods of testing pressure like hydraulic or aeronautical.

4. Special project requirements such as safety valves, isolation requirements and isometric graph codes.

📊 Special project modifications include:

Safety valves

Fire fighting lines

The requirements of isolation

Steering the edges

Requirements of Rolled Edges

𝐖𝐞𝐥𝐝𝐢𝐧𝐠 𝐃𝐞𝐟𝐞𝐜𝐭𝐬: 𝐀 𝐐𝐮𝐢𝐜𝐤 𝐆𝐮𝐢𝐝𝐞 𝐟𝐨𝐫 𝐄𝐧𝐠𝐢𝐧𝐞𝐞𝐫𝐬 𝐚𝐧𝐝 𝐖𝐞𝐥𝐝𝐞𝐫𝐬

Welding is a critical process in fabrication, but it's not without its challenges. Understanding common welding defects is essential for ensuring strong, reliable joints and maintaining structural integrity. Here's a quick look at 8 frequent welding defects every welder and engineer should be aware of:

𝟏. 𝐂𝐫𝐚𝐜𝐤

 Cracks are serious defects that weaken the weld and can propagate under stress, often caused by rapid cooling or high residual stresses.

𝟐. 𝐏𝐨𝐫𝐨𝐬𝐢𝐭𝐲

 Porosity appears as gas pockets or voids within the weld, usually due to contamination or improper shielding gas during welding.

𝟑. 𝐔𝐧𝐝𝐞𝐫𝐜𝐮𝐭

 Undercut occurs when the weld metal fails to fill the groove between the base metals, leaving a groove along the weld toe, reducing strength.

𝟒. 𝐂𝐨𝐥𝐥𝐚𝐩𝐬𝐞

 Collapse is a structural failure where the weld loses its profile due to excessive heat input or poor joint design.

𝟓. 𝐒𝐩𝐚𝐭𝐭𝐞𝐫

 Spatter consists of small metal droplets scattered around the weld area, often caused by high current or incorrect arc length.

𝟔. 𝐎𝐱𝐢𝐝𝐚𝐭𝐢𝐨𝐧 𝐁𝐥𝐚𝐜𝐤𝐞𝐧𝐢𝐧𝐠

 This defect results from exposure to air during welding, leading to discoloration and a weakened weld zone due to oxidation.

𝟕. 𝐁𝐮𝐫𝐧𝐢𝐧𝐠-𝐓𝐡𝐫𝐨𝐮𝐠𝐡

 Burn-through occurs when the base metal melts away, creating holes—often due to excessive heat or thin base material.

𝟖. 𝐏𝐨𝐫 𝐅𝐨𝐫𝐦𝐢𝐧𝐠

 Poor forming refers to improper weld shape or bead formation, affecting both aesthetics and strength of the joint.

📌 Ensuring proper technique, parameters, and joint preparation is key to avoiding these defects and achieving high-quality welds.

 Let’s keep building better, safer structures—one weld at a time

Pipe Size According to 2024 Global Standards

Pipe Line DZ

NPS – Nominal Pipe Size

An American standard (in inches, without unit symbols) used to define pipe size.

For example: NPS 2 has an outside diameter (OD) of 2.375 inches

For NPS 14, the OD is exactly 14 inches

The inside diameter varies depending on the wall thickness, specified by the Schedule (SCH)

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SCH – Schedule (Wall Thickness)

Defines the pipe wall thickness numerically:

📐 Schedules: 5, 10, 20, 40, 80, 160, XS, XXS

🧮 Formula: Schedule ≈ 1000 × (P / S)

P = Design Pressure (psi)

S = Allowable Stress (psi)

📚 Standard References:

ASME B36.10M (2024) for carbon/alloy steel pipes

ASME B36.19M (2024) for stainless steel pipes (symbolized as “S” in SCH numbers like 10S, 40S)

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DN – Diameter Nominal

A metric-based international pipe size standard by ISO (in mm, without “mm” symbol).

Equivalent to NPS as per ISO 1127:2024

🧾 Examples:

DN 15 = NPS ½

DN 50 = NPS 2

DN 300 = NPS 12

🧱 Wall Thickness Series:

Series 1, Series 2, Series 3

Used primarily for classifying stainless steel pipes (B36.19M)

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📊 Pipe Size Equivalents Table:

NPS DN OD (inches) Schedule

½ 15 0.840 SCH 80

2 50 2.375 SCH 40

14 350 14.000 SCH 60

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📎 References:

ASME B36.10M:2024

ASME B36.19M:2024

ISO 1127:2024

13 BOILER ESSENTIAL FITTING

As per the Factories Act and Boiler Regulations in India, some essential fittings for a boiler typically include:

1. Safety Valve

2. Pressure Gauge

3. Water Level Indicator

4. Feed Check Valve

5. Blowdown Valve

6. Fusible Plug

7. Steam Stop Valve

8. Feed Water Inlet

9. Manhole or Handhole Covers

10. Mud Drum (if applicable)

11. Superheater Safety Valve (if applicable)

12. Boiler Mountings (e.g., pressure gauge, water level gauge)

13. Drain Valve

These fittings ensure safe operation, monitoring, and maintenance of the boiler. Specific requirements may vary depending on the jurisdiction and type of boiler.

Why suction piping diameter is bigger than discharge in centrifugal pump❓

👉 In the world of fluid dynamics and mechanical engineering, centrifugal pumps play a crucial role in transporting liquids from one place to another. A key aspect of their design and operation is the sizing of the suction and discharge piping. Typically, the suction piping of a centrifugal pump is larger in diameter than the discharge piping. This design choice is not arbitrary but is based on several important principles of physics and engineering. Let's delve into why suction piping diameter is often bigger than the discharge piping in centrifugal pumps.

👉 Understanding Centrifugal Pumps
First, it's essential to understand how a centrifugal pump works. A centrifugal pump uses an impeller to add velocity to a liquid, which is then converted into flow. The liquid enters the pump through the suction inlet, where it is accelerated by the impeller and then discharged through the outlet. The efficiency and effectiveness of this process depend significantly on the design and sizing of the pump and its associated piping.

👉 The Role of Suction Piping
The suction piping is responsible for delivering the liquid to the pump. The primary goal here is to ensure that the liquid reaches the pump with minimal resistance and without causing cavitation, which is the formation of vapor cavities in a liquid due to low pressure. Cavitation can cause significant damage to the pump and reduce its efficiency.

👉 Why Larger Suction Piping?
1️⃣ Reducing Friction Losses: A larger diameter pipe results in lower fluid velocity, which in turn reduces friction losses. Lower friction losses mean that the liquid can flow more easily into the pump, reducing the energy required to move the liquid and minimizing the risk of cavitation.

2️⃣ Minimizing Pressure Drop: As liquid flows through a pipe, there is a natural drop in pressure due to friction and other factors. A larger diameter pipe helps to minimize this pressure drop, ensuring that the liquid reaches the pump at a higher pressure. This is crucial for maintaining the Net Positive Suction Head (NPSH), which is the difference between the pressure at the suction inlet and the vapor pressure of the liquid. Adequate NPSH is essential for preventing cavitation.

3️⃣ Enhancing Pump Efficiency: By reducing friction losses and minimizing pressure drop, a larger suction piping diameter helps to enhance the overall efficiency of the pump. This means that the pump can operate more effectively, with less energy consumption and reduced wear and tear.

4️⃣ Handling Viscous Liquids: When dealing with viscous liquids, which have a higher resistance to flow, a larger suction piping diameter becomes even more important. The increased diameter helps to accommodate the higher resistance and ensures smooth flow into the pump.

👉 The Role of Discharge Piping
The discharge piping, on the other hand, is responsible for transporting the liquid from the pump to its destination. The primary goal here is to deliver the liquid at the desired flow rate and pressure. A smaller diameter pipe is often used for discharge piping because it helps to maintain higher fluid velocity and pressure, which are essential for effective transportation and distribution of the liquid.

Pipe Welding Sites and Techniques - For Quality Control Engineers (QC)

In piping industry, welding is not only a manual skill, but a science and technology based on strict international standards.

🔍QC engineer responsible for inspecting welds and ensuring that they comply with codes such as ASME Section IX and AWS D1.1.1.

📌 Welding Positions:

🔧 These locations have been designated to ensure welders are tested in various conditions.

1. 1G - Flat Position:

🔹 The pipe is placed horizontal

🔹 A welder is only welding from above

2. 2G - Horizontal Position:

🔹 The pipe is in a vertical position

🔹 Welding is done horizontally on the side wall

3. 5G - Horizontal Fixed):

🔹 The tube is horizontal but cannot be rotated

🔹The welder works on the tube perimeter from bottom to top

4. 6G - Inclined at 45° and steady angle:

🔹 The pipe is fixed at a 45° angle and cannot be rotated

Welding works from all directions🔹

⚠️ The most difficult site, and is used to test the competence of welders because it mimics all situations.

5. 6GR - 6G with Restricted:

🔹 Like 6G but with obstacles that prevent the welding from moving freely.

🔹 Used in very critical work, such as ship structures or complex systems

🧠 Needs a very professional welder.

⚙️ Welding Techniques Used in Pipes (WP):

Each technique has its properties, and its selection depends on the type of material, tube thickness, and welding location (workshop or site).

1. SMAW (Shielded Metal Arc Welding)

🔸 Widely used in welding carbon steel pipes

🔸 Flexible and works well in outdoor sites

🔸 Suitable for difficult positions such as 5G and 6G.

2. GTAW (TIG – Tungsten Inert Gas):

🔸 Especially used in root passes (Root Pass)

🔸 Ideal for stainless steel (Stainless Steel)

🔸 Gives accurate and clean welders

🔸 It requires high skill.

3. FCAW (Flux Cored Arc Welding) / GMAW (MIG):

🔸 Used in workshops and factories

🔸 Provides high productivity

🔸 Less common in operation pipes due to the need to protect against gases and conditions.

Welding Procedure - WPS/ PQR According to ASME Section IX 

🔸 WPS (Welding Procedure Specification):

A document that shows the method of welding in detail (matter, position, electrode type, temperature, welding speed... Etc).

🔸 PQR (Procedure Qualification Record):

Demonstration documentation of WPS welding test results, includes mechanical, visual and non-destructive inspections.

Important tips for QC quality control engineers:

🔹 Always check the validity of your WPS documents - is it 5G or 6G mode?

🔹Watch the compatibility of Filler Metal with the basic metal

🔹Check the quality of the root pass accurately - it is the basis of good restraint

🔹 Do not forget to check the temperature preheat (Preheat) and post-weld Heat Treatment – PWHT) if found.

𝐖𝐡𝐚𝐭 𝐚𝐫𝐞 𝐓𝐚𝐧𝐤 𝐁𝐫𝐞𝐚𝐭𝐡𝐞𝐫 𝐕𝐚𝐥𝐯𝐞𝐬?

𝐖𝐡𝐚𝐭 𝐚𝐫𝐞 𝐓𝐚𝐧𝐤 𝐁𝐫𝐞𝐚𝐭𝐡𝐞𝐫 𝐕𝐚𝐥𝐯𝐞𝐬?

• Breather valves (vent valves) maintain safe pressure in storage tanks.
• Allow air in/out to regulate pressure/vacuum.

𝗜𝗺𝗽𝗼𝗿𝘁𝗮𝗻𝗰𝗲:
• Safety - Prevent catastrophic failures.
• Product Quality - Minimize contamination.
• Efficiency - Extend tank lifespan, reduce maintenance.

𝗧𝘆𝗽𝗲𝘀:
1. 𝙋𝙧𝙚𝙨𝙨𝙪𝙧𝙚-𝙊𝙣𝙡𝙮
  • Release excess pressure
  • Used for non-volatile liquids

2. 𝙑𝙖𝙘𝙪𝙪𝙢-𝙊𝙣𝙡𝙮
  • Allow air in during vacuum
  • Prevent implosion/damage

3. 𝙒𝙚𝙞𝙜𝙝𝙩-𝙇𝙤𝙖𝙙𝙚𝙙
  • Use adjustable weights to open/close
  • Reliable, adjustable

4. 𝙋𝙞𝙡𝙤𝙩-𝙊𝙥𝙚𝙧𝙖𝙩𝙚𝙙
  • Use pilot system for precise control
  • Rapid response, complex systems

5. 𝙋𝙧𝙚𝙨𝙨𝙪𝙧𝙚 & 𝙑𝙖𝙘𝙪𝙪𝙢
  • Handle over/under pressure
  • Used for various applications

Major Global Hydrogen Deals happened during Jun24

Nox Emissions and their Impact

Emissions of oxides of nitrogen, commonly referred collectively as NOx, are regulated because of their adverse effects on health and the environment. They play an important role in acid rain, the formation of harmful ozone and photochemical smog in the lower atmosphere and the depletion of the beneficial ozone in the upper atmosphere.

The most environmentally important oxides of nitrogen are:

NO, NO2, and, more recently, N2O.

N2O is a recent concern because it is a "greenhouse" gas which contributes to global warming and because it can aid in destroying the upper atmosphere ozone layer which protects us from ultraviolet radiation. Fortunately, very little N2O is emitted from the flame of a typical burner.

Over 90% of the NOx from a typical flame is in the form of NO and the remainder is NO2. However, since NO is eventually converted to NO2 in the atmosphere, most regulations treat all of the NOx as NO2.

NOx emissions from combustion sources are due to the oxidation of atmospheric N2 and the oxidation of nitrogen chemically bound in fuel molecules. Mechanisms for forming NO include the fuel NOx, prompt NOx and thermal NOx mechanisms. Some of these mechanisms are well understood, while others are still under investigation.

Although NO and NO2 molecules last only a matter of days in the atmosphere, N2O is a very stable species that can last 100 to 200 years in the lower atmosphere. Because of its long life span some N2O eventually reaches the upper atmosphere where it decomposes under ultra violet light and it's reaction products efficiently remove ozone from the upper atmosphere.

A Marley mechanical induced draft cooling tower

 

The heat absorbed by the circulating cooling water in the condenser tubes must also be removed to maintain the ability of the water to cool as it circulates.

This is done by pumping the warm water from the condenser through either natural draft, forced draft or induced draft cooling towers.

The cooling water used to condense the steam in the condenser returns to its source without having been changed other than having been warmed. If the water returns to a local water body (rather than a circulating cooling tower), it is tempered with cool 'raw' water to prevent thermal shock when discharged into that body of water.

Another form of condensing system is the air-cooled condenser. The process is similar to that of a radiator and fan. Exhaust heat from the low pressure section of a steam turbine runs through the condensing tubes, the tubes are usually finned and ambient air is pushed through the fins with the help of a large fan. The steam condenses to water to be reused in the water-steam cycle. Air-cooled condensers typically operate at a higher temperature than water cooled versions. Whilst saving water, the efficiency of the cycle is reduced (resulting in more carbon dioxide per MW of electricity).

Thermal Storage Walls

 A thermal storage wall is a passive solar heating system in which the primary thermal storage medium is placed directly behind the glazings of the solar aperture. The outer surface of the massive wall is painted a dark color or coated with a selective surface to promote absorption of solar radiation. Solar radiation absorbed on the outer surface of the wall is converted to heat and conducted (or convected in the case of the water walls) to the inner surface where it is radiated and convected to the living space. Heat transfer to the living space is sometimes augmented by the addition of circulation vents placed at the top and bottom of the mass wall. These vents function in the same manner as the vents in a TAP system except that only a portion of the solar heat delivered by the system passes through the vents.

A thermal storage wall provides an effective buffer between outside ambient conditions and the building interior; night time heat losses are reduced during the cold winter months, and during the summer, unwanted heat gains are limited. This moderating effect generally enables thermal storage walls to outperform direct gain systems. There are many types of thermal storage walls distinguished by the type of storage medium employed.

 

Trombe Wall. A Trombe wall is a thermal storage wall that employs solid, high density masonry as the primary thermal storage medium. Appropriate thicknesses range from 6 to 18 inches depending on the solar availability at the building site. Sunny climates require relatively thicker walls due to the increased thermal storage requirements. The wall may be vented or unvented. A vented wall is slightly more efficient and provides a quicker warm up in the morning but may overheat buildings

containing little secondary thermal storage mass in the living space.

 

Concrete Block Wall. Ordinarily, a thermal storage wall would not be constructed of concrete building blocks, because solid masonry walls have a higher heat capacity and yield better performance. However, where concrete block buildings are very common they may offer opportunities for passive solar retrofits. The south facing wall of a concrete block building can be converted to a thermal storage wall by simply painting the block a dark color and covering it with one or more layers of glazing. Walls receiving this treatment yield a net heat gain to the building that usually covers the retrofit costs rather quickly. The relatively low heat capacity of concrete block walls is offset somewhat by the large amount of secondary thermal storage mass usually available in these buildings. Concrete floor slabs and massive partitions between zones help prevent overheating and otherwise improve the performance of concrete block thermal storage walls. Concrete block thermal storage walls may also be introduced during the construction of new buildings. For new construction, however, it is advisable to take advantage of the superior performance of solid masonry walls by filling the cores of the block in the thermal storage wall with mortar as it is erected. This process is inexpensive and the resulting performance increment covers the increased cost. The design procedures developed herein are applicable to 8-inch concrete block thermal storage walls with filled or unfilled cores.

 

Water Wall. Water walls are thermal storage walls that use containers of water placed directly behind the aperture glazings as the thermal storage medium. The advantage over masonry walls is that water has a volumetric heat capacity about twice that of high density concrete; it is therefore possible to achieve the same heat

capacity available in a Trombe wall while using only half the space. Furthermore, a water

wall can be effective at much higher heat capacities than a Trombe wall because natural convection within the container leads to an nearly isothermal condition that utilizes all of the water regardless of the wall thickness. The high thermal storage capacity of water walls makes them especially appropriate in climates that have a lot of sunshine.

Transpired collector - Energy-Saving Mechanism

 A transpired collector reduces the load on a building’s heating system by heating intake air with solar energy. It preheats the ambient air by up to 40°F, reducing all or a portion of the load on a heating system during daylight hours. Although the transpired collector itself may not be able to achieve the required indoor air temperature on cloudy days or when the outside temperature plummets, it still provides useful energy and reduces utility bills.

The dark-coloured transpired collector is a large solar collector, absorbing the solar energy striking it. The wall captures between 60% and 75% of the available solar energy, making it one of the most efficient solar collectors designed to date. In addition to capturing direct solar radiation, the transpired collector collects the indirect, scattered, and reflected sunlight known as diffuse solar radiation. Typically, diffuse solar radiation, which includes a portion of the radiation on clear days and all the radiation on overcast days, makes up about 25% of the total annual radiation at the Earth’s surface.

The dark, corrugated metal sheets that make up the wall are 0.8-millimeter (mm)-thick and are typically manufactured from aluminium or galvanized steel. The perforations through which the air flows are 1.6 mm in diameter and are placed at regular intervals. The total percentage of the collector made up of these holes is referred to as the collector porosity.

Transpired collector operation during the winter months.

Transpired collector operation during the summer months.

Heat transfer fluid contained in the collector loop

 Heat transfer fluid contained in the collector loop are :

 

WATER. As a heat transfer fluid, good quality water offers many advantages. It

is safe, non-toxic, chemically stable, inexpensive, and a good heat transfer medium.

Two drawbacks include a relatively high freezing point and a low boiling point.

Excessive scaling may occur if poor quality water is used.

 

GLYCOLS. Propylene or ethylene glycol is often mixed with water to form an

antifreeze solution. Propylene glycol has the distinct advantage of being nontoxic,

whereas ethylene glycol is toxic and extreme caution must be used to ensure that it is isolated from any potable water. For this reason, uninhibited USP/food-grade propylene glycol and water solution will be specified for any solar preheat system that requires an antifreeze solution.

Linear Fresnel Solar Collector

 

Solar thermal energy collection system

A solar thermal energy collection system is defined as a set of equipment that intercepts incident solar radiation and stores it as useful thermal energy to offset or eliminate the need for fossil fuel consumption. Four basic functions are performed by a typical solar system.

COLLECTOR SUB-SYSTEM. The collector sub-system intercepts incident solar

radiation and transfers it as thermal energy to a working fluid. It is defined as the solar

collector, the hardware necessary to support the solar collector, and all interconnecting

piping and fittings required on the exterior of the building housing the system.

 

STORAGE SUB-SYSTEM. The storage sub-system retains collected thermal

energy for later use by the process load. It is defined as the storage tank and its fittings

as well as other necessary supports.

 

TRANSPORT SUB-SYSTEM. The transport sub-system delivers energy from the

collectors to storage. This sub-system is defined to include the heat transfer (or

working) fluid, pump(s), the remaining system piping and fittings, an expansion tank,

and a heat exchanger (if required).

 

CONTROL SUB-SYSTEM. The control sub-system must first determine when

enough energy is available for collection. It must then activate the entire system to

collect this energy until it is no longer available as a net energy gain. The control

subsystem thus consists of electronic temperature sensors, a main controlling unit that

analyzes the data available from the temperature sensors, and the particular control

strategy used by the controller.

Sunspaces

 There are many possible configurations for a sunspace but all of them share certain basic characteristics. Sunlight enters the sunspace through south facing glazing that may be vertical or inclined or a combination of the two and is absorbed primarily on mass surfaces within the enclosure; the mass may be masonry or water in appropriate containers and is generally located along the north wall and in the floor. The massive elements provide thermal storage that moderates the temperature in the enclosure and the rate of heat delivery to the living space located behind the north wall. Operable windows and circulation vents in the north wall provide for heat transfer by thermal convection from the sunspace to the living space. The north wall may be an insulated stud wall placed behind containers of water or a masonry wall through which some of the heat in the sunspace is delivered to the building interior by thermal conduction as occurs in a Trombe wall. A sunspace may be semi-enclosed by the main structure such that only the south facing aperture is exposed to ambient air, or may be simply attached to the main structure along the north wall of the sunroom, leaving the end walls exposed.

COLLECTOR EFFICIENCY AND PERFORMANCE

 

Collector efficiency is defined as the fraction of solar energy

incident upon the face of the collector that is removed by the fluid circulating through the collector. Several parameters are defined as follows:

Ti = heat transfer fluid inlet temperature

Ta = ambient air temperature

I = solar irradiance on the collector

Ac = solar collector surface area

FR = collector heat removal factor, a dimensionless parameter describing the ratio

of actual energy gained by the collector to that which would be gained, in

the limit, as the absorber plate temperature approaches the fluid inlet

temperature. This value is similar to a conventional heat exchanger's

effectiveness.

UL = overall heat loss coefficient. This factor describes the cumulative heat

transfer between the collector and the ambient surroundings.

t = transmittance of the glazing.

a = absorption coefficient for the absorber plate. Note that this value varies with

wavelength. A selective surface is one that absorbs short wavelength solar

radiation very well while emitting longer wavelength thermal radiation poorly.

Thermosiphoning Air Panels

 Thermosiphoning Air Panels. Thermosiphoning air panels (TAPs) are also appropriate for use on metal buildings either as retrofits or in new construction. Two configurations occur in practice and the first, which is referred to as a frontflow system. Again there are one or more glazing layers over an absorbing metal surface but, in this case, the metal panel is insulated on the back side. Heat

transfer to the interior occurs via circulation vents cut through the metal panel and its insulation at the upper and lower extremes. Solar radiation absorbed on the the outer surface of the panel is converted to heat and convected to the adjacent air which then rises due to buoyancy forces and passes through the upper vent into the living space. The warm air leaving the gap between the inner glazings and the absorber is replaced by cooler air from the building interior that enters through the lower vents. In this manner, a buoyancy driven loop is established and sustained as long as the temperature in the air gap exceeds that in the living space. Passive backdraft dampers or manually operated vent closures must be employed to prevent reverse circulation at night. Backdraft dampers are usually made of a lightweight plastic material suspended above a metal grid such that air flows freely in one direction but is blocked should the flow attempt to reverse.

The second type of TAP configuration is called a backflow system. In a backflow system, the flow channel is behind the absorber plate rather than in front of it. An insulated stud wall is constructed a few inches behind the metal panel and vents are then cut at the top and bottom of the wall. Air in the flow channel thus formed is heated by convection from the back of the absorber panel and a circulation loop is established in the same manner as in a front flow system.

TAPs have thermal storage requirements similar to those of direct gain and radiant panel systems. Generally speaking, the best performance will be obtained from passive solar systems associated with high heat capacity structures. Although a backflow TAP performs slightly better than a comparable system in the frontflow configuration, the difference is not significant and construction costs should govern any choice between the two. Both TAP configurations outperform radiant panels and direct gain systems with comparable glazings and thermal storage mass. This performance edge is due to the low aperture conductance of TAPs, which can be insulated to arbitrary levels, thereby limiting night time heat loss.

Radiant Panels for Homes

 Radiant Panels

Radiant panels are simple passive solar systems that are inexpensive and well suited as retrofits to metal buildings. Note that the solar aperture consists of one or more layers of glazing material placed over an uninsulated metal panel. The metal panel would ordinarily be a part of the building shell so that a retrofit is constructed by simply glazing an appropriate area on the south side of the structure. Any insulation or other poorly conducting material should be removed from the inner surface of the glazed portion of the metal panel to facilitate heat transfer to the interior.

 

Solar radiation is absorbed on the outer surface of the metal panel after passing through the glazings. The panel becomes hot and gives up heat to the interior by radiation and convection. Thermal mass must be included inside the building shell as with direct gain systems. Usually, only a concrete slab will be available before retrofitting a metal building and it may sometimes be necessary to add water containers to achieve the desired thermal capacitance. Radiant panels perform on a par with direct gain buildings and are likely to be less expensive when used as retrofits to metal buildings.