InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website. Our page top photo shows how individual office occupants who are too hot or too cold can foul up carefully balanced air distribution in a building. Just push over a section of suspended ceiling. HVAC duct air flow balance means that we have adjusted the flow through the air duct system such that we get the desired quantity of cool or warm air in all of a building's occupied spaces.
If the duct air flow system is out of balance you will find that when heating, some rooms are not warm enough while others are too cool. While in cooling or air conditioning mode you'll find similarly that some rooms are not cool enough while others are too warm. When ductwork runs like a crazy twisting worm all through an attic its unnecessary length and extra sinuous bends and crips can seriously block air flow to some building areas.
Generally we want to keep ductwork as short and direct as possible. You may want your service person to review air flow in different rooms, to add manual balancing dampers in the duct system and show you where they are located and mark on the duct just where the balancing damper levers are normally set.
The photographs above show both supply and return ceiling registers in a commercial office space. In this case they are located too close together. The second photograph above right shows that a ceiling tile has been removed from a suspended ceiling over an office which uses the ceiling cavity as a common return air plenum.
While this may produce more airflow in the office where this suspended ceiling tile was removed, it has unbalanced the entire air conditioning system for the rest of the offices in the building.
Many commercial spaces and offices are cooled and sometimes heated as well by an air handler which delivers supply air to each office area by flex duct connected to ceiling registers. Return air is passed back to the air handler through the large common space above a suspended ceiling over the occupied space. Special vents either around the supply registers or placed separately are intended to pass return air to the common ceiling space, and their location and adjustment are important to provide balanced airflow in the work space.
Use of a single return air location invites un-balanced air flow delivery into various rooms in a building, especially if room doors are left shut and there is no provision for air movement out of closed rooms to the central return register. In addition, distance to the central return air register, obstructions, or circuitous routing through hallways or even among different floors in a building all argue that a single central return air register can contribute to an air-starved air handler or uneven air delivery to the conditioned spaces.
This photograph shows a common ceiling plenum over a commercial office space in a Manhattan high rise building. Notice the considerable amount of debris atop the ceiling tiles? All of the office conditioned air moves through this area, risking additional levels of irritating or harmful particles, particularly if the debris contains asbestos fragments or lead paint chips. In this particular case tests showed that this was not the case.
These photos show a common ceiling return air plenum over commercial offices. In the first or left hand photo, notice that rectangular opening in the distance? The second photo is a close-up showing a big surprise: the ceiling area used as return air plenum for an office suite is wide open to the rest of the building ceilings on the same floor.
Openings had been left open between the office space and the top floor hallway and also between the hallway and other office spaces in the building, so that particles, leak-related mold, or other irritating particles developing over any office will be shared among all of the tenants on this building floor. Watch out : unanticipated or improper openings between building areas may also be a fire hazard, contributing to the rapid spread of fire from one building area to another.
Missing or incomplete ceiling partitioning in large commercial buildings may mix air and odors or contaminants from multiple offices or building use areas, redistributing these un-wanted odors or particles to other building areas. One of our clients who maintained a law office in a strip mall complained of chemical odors which were traced to a beauty parlor located at the extreme other end of the building.
Open windowsespecially in a tall office building such as shown by this photograph, cause a tremendous up-draft through the building, moving particles, gases, or other potential IAQ concerns up through the building.A chemical equation is a written description of what happens in a chemical reaction. The starting materials, called reactantsare listed on the lefthand side of the equation. Next comes an arrow that indicates the direction of the reaction. The righthand side of the reaction lists the substances that are made, called products.
A balanced chemical equation tells you the amounts of reactants and products needed to satisfy the Law of Conservation of Mass. Basically, this means there are the same numbers of each type of atoms on the left side of the equation as there are on the right side of the equation.
It sounds like it should be simple to balance equationsbut it's a skill that takes practice. So, while you might feel like a dummy, you're not!Percent Excess Air (Combustion)
Here's the process you follow, step by step, to balance equations. You can apply these same steps to balance any unbalanced chemical equation The first step is to write down the unbalanced chemical equation. If you're lucky, this will be given to you. If you're told to balance a chemical equation and only given the names of the products and reactants, you'll need to either look them up or apply rules of naming compounds to determine their formulas.
Let's practice using a reaction from real life, the rusting of iron in the air. To write the reaction, you need to identify the reactants iron and oxygen and the products rust. Next, write the unbalanced chemical equation:. Note the reactants always go on the left side of the arrow. A "plus" sign separates them. Next, there is an arrow indicating the direction of the reaction reactants become products.
The products are always on the right side of the arrow. The order in which you write the reactants and products is not important. The next step for balancing the chemical equation is to determine how many atoms of each element are present on each side of the arrow:. To do this, keep in mind a subscript indicates the number of atoms. For example, O 2 has 2 atoms of oxygen. There are 2 atoms of iron and 3 atoms of oxygen in Fe 2 O 3. There is 1 atom in Fe.
When there is no subscript, it means there is 1 atom. How do you know the equation isn't already balanced? Because the number of atoms on each side isn't the same! Conservation of Mass states mass isn't created or destroyed in a chemical reaction, so you need to add coefficients in front of the chemical formulas to adjust the number of atoms so they will be the same on both sides.
When balancing equations, you never change subscripts. You add coefficients. Coefficients are whole number multipliers. If, for example, you write 2 H 2 O, that means you have 2 times the number of atoms in each water molecule, which would be 4 hydrogen atoms and 2 oxygen atoms. As with subscripts, you don't write the coefficient of "1", so if you don't see a coefficient, it means there is one molecule.When you start hearing chatter about the building being hot and humid, drafty, smoky or uncomfortable, you know a problem has already taken root.
In addition to unhappy customers and employees, these comfort issues typically are indicators of energy inefficiency within a system. So, what can facility managers do to prevent comfort and energy threats?
A good place to start is to gain a foundational understanding of building pressure and common HVAC deficiencies along with following seven easy steps to bring your restaurant back into tune. Most importantly, learn how to look for negative building pressure. Remember, the goal is to stay slightly positive in building pressure.
There are three methods to identify negative building pressure. The first and most reactive method is to monitor signals that your building is negative. What causes a building to become negative or unbalanced? The usual offenders are equipment deficiencies, improper preventative maintenance programs, and adjustment errors such as kitchen staff fiddling with thermostats or service contractors opening or closing dampers.
These steps may be completed by the facility manager alone, but are more likely in partnership with a service contractor. One Principal Engineer at a hamburger fast food chain overseeing thousands of locations explains how her team uses the air balance report to get started with troubleshooting comfort issues.
I look at the punch list and ask was anything wrong? Not fixed? It helps when I have to remotely assess or diagnose problems. Whether the previous air balance report has been reviewed or not, proceed to the following steps:. Tagged: Tags: HVACair balancetest and balance hvactab hvacair flow hvacbalance hvac systemtest tabtab contractortab services.
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Skip to content. Second, you can measure the building pressure yourself or with the help of your service contractor by using a pressure reading tool such as an anemometer to get a ballpark pressure reading. If comfort-related issues or a negative building pressure reading are observed, then an air balance needs to be scheduled. Investigating the Cause What causes a building to become negative or unbalanced?
Turn on all HVAC equipment. Are there drafts along the cook line? Inspect the equipment. Are the filters clean? Are the belts in good condition? Are the exhaust fan wheels clean?
Example of an HVAC installer’s balancing report form
Determine an intervention plan. If equipment is inoperable, have it repaired or replaced. If the preventative maintenance actions are in order and the problems persist, call in a certified air balance company that has experience with restaurants like yours.
Facility managers need to trust that their service contractors will notify them of airflow-related issues.Using 1 the sensible heat added to the air can be calculated as. An air flow of 1 cfm is heated from 32 to 52 o F. Using 1b the sensible heat added to the air can be calculated as. Sensible heat load and required air volume to keep the temperature constant at various temperature differences between make up air and room air:.
An air flow of 1 cfm is cooled from 52 to 32 o F. Latent heat load - humidifying and dehumidifying - and required air volume to keep temperature constant at various temperature differences between entering air and room air are indicated in the chart below:.
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Calculating Aircraft Weight and Balance
Join Eng-Tips Forums! Join Us! By joining you are opting in to receive e-mail. Promoting, selling, recruiting, coursework and thesis posting is forbidden. Students Click Here. Related Projects. How to make a detailed air balance calculations? Conservation of mass. In a conventional system, the zone will be pressurized via outside air introduced into the return air path. This results in the excess air being lost to the structure and thus the zone is at a positive pressure in relation to outside environment.
This OA introduction is used to ventilate the space or control directional air flow from a quality point of view. This appears to be a designers schedule to instruct the balancer to setup the system, verify code compliance for ventilation and or owners design objectives. This is a poorly developed table due to the notes do not call out the use of an exhaust fan. Most designers will separate the exhaust flow from a return air path. The space will leak in or out based upon the integrity of the pressure boundary of the envelope and the DP.
You use the term calculate, do you mean measure? First off the balancer list just reflects the air balance as shown on the HVAC drawings. Pressurization offsets infiltration so the building is positive. We usually estimate this to he 0. However for clean or dirty areas it would be about CFM per door. This is based on no leakage through the normally closed relief air damper which would be open during outdoor air economizer cycle.
Actual design minimum OA would be the larger value based on the above. Red Flag This Post Please let us know here why this post is inappropriate.This instructable explains the process of finding the center of gravity for the weight and balance of an aircraft. This is an important process when piloting an aircraft because the location affects performance characteristics of the aircraft and if it is out of acceptable limits the aircraft may be uncontrollable.
Having this information calculated and on hand is, in fact, a requirement for every flight you make. Did you use this instructable in your classroom? Add a Teacher Note to share how you incorporated it into your lesson. Each aircraft's weight and moment are different.
It will be in the weight and balance chapter which is standard chapter six. This includes pilot, all passengers, baggage, and the fuel that will be loaded into the aircraft. You will find the fuel load in the first chapter of the POH. Keep in mind that you will use the amount labeled "usable fuel" because unusable fuel is included in the aircraft's weight and that fuel weighs six pounds per gallon.
In chapter 6 of the POH you will find either a chart similar to the one on the left or a figure like the one shown on the right.
If you have the chart you can follow the weight to the appropriate line to find the moment. If you have the figure, you need to multiply the weight of each position by the number given as the arm to find the moment.
Calculate the moments for the pilot, all passengers, fuel, and baggage. Using the graph above, if the pilot and front passenger weighed pounds, you would find on the vertical axis. You then follow that over to where it intersects the line labelled "Pilot and front passenger".
You then follow that down to the horizontal axis to get your moment value of about Add together the weights for the aircraft, people, fuel, and baggage. Also add the moments found in the previous step pilot, passengers, fuel, and baggage to the moment of the empty aircraft. In chapter 6 of the POH find the chart that shows the acceptable limits of the center of gravity.
It will look like one of the charts pictured above.Air and water balancing is a method of regulating HVAC air supply, return, and exhaust, or the flow of water through coils, to achieve a neutrally balanced, comfortably conditioned commercial, institutional or industrial building. Improper balance can result in poor indoor air quality, occupant discomfort, and system inefficiency.
Fortunately, these types of HVAC issues can usually be easily remedied through professional air and water balancing, otherwise known as TAB testing, adjusting and balancing. There are a number of symptoms to look for that can warrant hiring a TAB specialist such as MSC to perform air and water balancing. These include:. Air naturally flows from positive to negative areas wherever there is a differential in pressure. A negative building that brings in less air than it exhausts will draw air through cracks, windows, open doors, and other openings, making it difficult to maintain comfortable conditions.
Conversely, excessive energy is required when more make-up air is brought in than is exhausted. Almost all existing HVAC systems can benefit significantly from air and water balancing.
A TAB professional will conduct a careful system analysis using a detailed checklist to determine where corrections should be made. Water balancing requires a similarly meticulous analysis of water flow through hydronic systems.
TAB is performed during retro-commissioning as part of a larger process that verifies temperature, humidification and pressurization in addition to air and water flow.
Air and water balancing usually uncovers a combination of issues that can have a negative effect on system performance. Many of the most common problems uncovered in these analyses, which are listed on page two, can be corrected easily and inexpensively. Buildings and facilities that undergo professional air and water balancing can expect to see significant improvements in occupant comfort, increased energy efficiency, and lowered utility bills.
Now more than ever, building owners and operators are making the simple investment into air and water balancing. Taking a holistic approach to how buildings and systems operate is a key component to system efficiency. Small adjustments and repairs are minor expenses that can have a large impact on return on investment, though it has been our experience that there will always be those who will ignore the symptoms of poor system performance.
They will suffer discomfort, pay higher utility bills, have reduced equipment life, replace equipment prematurely, and make unnecessary and expensive repairs when all that may be needed is a little attention. Invariably it is an accumulation of small issues and much-needed repairs that, when diagnosed and fixed properly, can bring the system or building back to its original design intent.
Most of these repairs can be made during the TAB process, which should always be performed by a technician with in-depth knowledge across multiple disciplines.
Always hire a certified pro, especially one with retro-commissioning experience, like MSC. A superior TAB contractor will provide a detailed diagnostic report along with all readings and settings clearly documented. This allows a system owner an excellent working knowledge of how systems should run and what parameters to check each season. Buyer beware of the contractor that is not really listening to your problems or suggesting how to correct them.
Taking care of what you have, repairing what is fixable, and properly maintaining systems through preventive maintenance is always the way to go. Mechanical Service Corp.
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