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ventilation requirements for refrigerating machinery rooms.

by:Lepu Seal     2019-11-10
Section 8 introduction. 11.
5 of ASHRAE standard 15 (ASHRAE 2010)
Status: \"The mechanical ventilation required to discharge refrigerant accumulation due to system rupture leakage will be able to or discharge air from the machine room in no less than the following quantities: Q = 100 [
Square root of G(Q = 70[
Square root of G)
Where Q = cubic feet of air flow per minute (
Liters per second)
G = mass of refrigerant (lbs)kilograms)
In large systems, any part is located in the computer room.
Standard 15 User Manual (
Fenton and Richards 2002
It is stated that the ventilation requirements table on which the formula is based may have been developed by 1930. In fact, Brown(2005)
Shows that the table appears for the first time in New York City code 1927 (
Article 18 section 220th)
And gives a history of the development of some other ventilation requirements.
This form did not appear in ASRE handbook until 1939 was adopted by the then B9 Committee and was modified.
These improvements include a higher ventilation rate for systems that exceed 1000 of refrigerant (Brown 2005).
There are several fundamental flaws in the standard type 15: 1)
The equation does not take into account the change of the maximum accepted concentration (
Or recommended concentration limit--RCL); 2)
The equation does not take into account the differences in cold storage properties such as boiling point, steam pressure and molecular weight; and 3)
Different room sizes are not considered.
This study was carried out to improve the standard 15 equation.
First, a review of the accident history associated with the refrigerant leakage in the computer room was made to help determine the economic, but reasonable scenario for future accidents.
Next, a differential equation was developed to estimate the ventilation rate to limit the concentration of refrigerant to the maximum limit of the proposed accident scenario.
Finally, to facilitate the application and implementation of the standard, we derive a simplified formula.
The purpose is to establish a technical basis for the specific ventilation requirements of the refrigeration room to maintain safety and to develop equations or other methods for calculating the required ventilation rate.
In order to achieve this goal, the ventilation strategy and rate required to minimize the health risks caused by leakage are based on realistic accident scenarios, reflecting the basic principles of dilution, consider the recommended concentration limits and physical properties of each refrigerant, and use them simply enough in standards and building codes that determine the ventilation requirements of the refrigeration room.
An overview of several databases in the background reveals the release scenario, including the number, duration, location in the system, and the reason for the release.
Some suggested their opinion on the actual release used to calculate ventilation needs.
The reported accident finding historical refrigerant leakage produced directions to determine the reality and appropriate accident scenarios that ventilation needs can be based on.
All accidents recorded in North America and Europe are considered to be accidents related to the leakage of refrigerant in the cabin, including the extent of the leakage, the cause, and any related damage to personnel or property.
Four major databases have been searched: * MARS (
Reporting system for major accidents)(MAHB 2001)
: Database of \"major accidents\" reported by Seveso, OECD and UN
Bureau of major accidents (MAHB).
The current MARSdatabase contains more than 700 accidents and attempted accidents collected from European Union member states since 1982.
A total of 17 accidents were considered between May 1991 and December 2001. * NRC (
National Response Center)(NRC 2010)
: NRC provides an annual data file containing event-related data (
Petroleum, chemical, radioactive, Biological
Logic and cause release of the United States and its territory).
Table 1 shows the number of reports submitted to the NRC (2010)
Regarding the above refrigerant that may be in the computer room.
Number of reports available (RQ)(US EPA 2001)
Is the number of thresholds that the law must report to the NRC for accumulated losses in the region within 24 hours.
Ammonia is the only refrigerant with a low enough amount to be reported.
So almost all accidents are ammonia.
The ARIP database also includes unexpected releases of some reports. * ARIP (
Unexpected release information program)(US EPA 2010)
: ARIP is a database compiled by EPA that focuses on the release of accidents caused in fixed facilities
The consequences of environmental damage. All non-
Regular emissions of oil and chemicals to be reported (
NRC, Coast Guard or EPA regional office).
Environmental Protection Agency of the United States (EPA)
Compile these electronic ports into the emergency response notification system (ERNS)database.
Select a major accident from the ERNS database according to the unexpected release information plan (ARIP)
A questionnaire was sent to the relevant facilities, including 23 questions about the facilities, the circumstances and causes of the incident, and the unexpected release of preventive practices and techniques in place by priorto, and add or change due to the event.
The ARIP database searched for accidents involving indoor refrigerant release from 1990 to 1999.
As EPA obtains information from the NRC database, most of the accidents found in the ARIP database also appear in the NRC database.
However, the ARIP database provides more detailed information about the reason for the release and the number of releases and the duration of the release.
Therefore, if possible, the information extracted from the ARIPdatabase is supplemented by the NRC data in order to provide as much information as possible for each event.
If the NRC database conflicts with the ARIP database, it is assumed that the ARIP database is more accurate.
223 accidents that met the standards were recorded. * OSHA (
Occupational Safety and Health Authority)(OSHA2010)
: The OSHA database focuses on accidents affecting workers and includes a summary of the accident investigation.
The accident investigation summary database records in detail accidents affecting workers and has limited information on the cause of chemical release, release duration, or number of releases.
A search was conducted and accidents involving the release of indoor refrigerant from January 1990 to February 2010 were extracted, resulting in 94 applicable accidents.
80 of them are reported to be ammonia.
The number of published information is limited. * NIOSH (
National Institute of Occupational Safety and Health)(NIOSH 2010)
Centers for Disease Control (CDC)
NIOSH reported the deaths of some accidents.
Mainly the workplace)
Through Death Assessment and Control Assessment (FACE)program.
Only one fat was found related to the refrigeration leak.
At 1992 in Alaska, an assistant ice rink manager died of suffocation while trying to stop aCFC
Leakage of the compressor interior.
All the databases listed are analyzed to identify unexpected situations that are conservative but may occur in standard practice.
The ARIP/NRC database is the most comprehensive.
Number of releases, duration of releases, and release parameters (
Gas, liquid, etc. )
It is listed as most accident reports.
Unfortunately, most ammonia accidents are recorded (see Table 2.
The most common release varies between 100 and pound.
The number of releases was classified and counted.
The probability distribution of emission rate is shown in Figure 1. [
Figure 1 slightly]
As shown in Figure 2, accidents seem to be more frequent before 1993.
On 1992, OSHA released the process safety management (PSM)
Standard for highly hazardous chemicals (OSHA 1992)
, Which contains process-related hazard management requirements for the use of highly hazardous chemicals.
For refrigeration systems, this standard is applicable to systems with an ammonia content of 10,000 pounds.
Any facility with an ammonia threshold must have an sms program.
All new facilities need to be planned and implemented before the introduction of ammonia exceeding the threshold. [
Figure 2:
Table 2 lists total emissions exceeding a specific probability.
These emission rates are worth it through linear insertion.
Of all accidents assessed, the total emission rate of 1% was greater than 2. 99 kg/s (395. 9 lb/min).
5% of the total accident emissions are greater than 1. 13 kg/s (149. 7 lb/min).
So far, no distinction has been made based on the release type (
Gas, liquid or both).
Figure 3 shows the sections of the different version types in the ARIP/NRC database.
Gas ammonia was reportedly released in 75% of the accidents, and only 13% involved pure liquid release.
But the boiling point of ammonia is 242 k (-28[degrees]F).
In most computer room environments, the liquid pool of ammonia produces steam due to heat transfer from the floor to the liquid.
So even pure liquid release will have a gas component.
On the other hand, liquid release may be mistaken for agaseous release, because the sudden pressure drop at the release point causes a portion of the liquid jet to turn into steam, and the remaining liquid may evaporate almost immediately.
Figure 4 shows the percentage of different reasons for the reported release.
Equipment failure is the main cause of the accident.
Calculating the average emission rate for all releases causes in0. 27 kg/s (35. 7 lb/min)
0 for operator error. 27 kg/s (35. 7 lb/min)
For equipment failure and 0. 16 kg/s (21. 2 lb/min)for other.
Therefore, due to equipment failure or operator error, the size of the release cannot be distinguished.
The ARIP database also details the location of the release.
The MARS and osha databases were also evaluated.
Both the OSHA and Mars databases have a large portion of unknown locations.
Even if the launch rate information is not given, the release location is listed, and Figure 5 shows the proportion of the occurrence of different release locations.
The most common leak is at the valve.
The second most likely location is the pipe.
While the total mass of the refrigerant is not as important as the emission rate, it plays a role in the analysis because it provides a rich limit on the amount of released refrigerant.
This leads to the discharge time, and increased ventilation may slow down the increase in refrigerant concentration in the room, but ventilation does not clear the room until the leak stops or all mass releases.
The upper limit is usually defined by the catastrophic failure of the largest vessel in the cabin.
If a large rupture occurs at the bottom, the amount of cold storage stored in this container can be released.
The released refrigerant will consist of the initial flash gas and the remaining liquid.
Due to the heat transfer from the floor to the liquid, the liquid pool, the mechanical room floor produces steam.
After a period of time, as the floor cools and approaches the equilibrium temperature of the refrigerant at atmospheric pressure, the steam generation rate will decrease with the heat transfer of the air above the liquid surface.
Another failure that could cause a large amount of release is a large breakdown in the liquid supply line.
If the flow does not stop, the production line can discharge a large amount of liquid.
Several incidents occurred in this way, resulting in the release of a large amount of ammonia.
In commercial buildings with refrigeration rooms equipped with chillers, smaller release events are similar to those of ammonia in industrial systems.
Failure of valve packaging, leakage of mechanical seals, failure of pipe and pipe fittings, corrosion failure or incorrect operation or maintenance procedures can result in these leaks.
Refrigerant storage containers are generally not used with chillers, so the number of refrigerants in these systems (R-11, R-22, R-123, R-134a, etc. )isconsider-ably less.
Therefore, the maximum cooling capacity of the chiller is much smaller than the potential capacity of the industrial facility.
General refrigerant release type. Brown (2005), Stoecker (1998), Richards (1986)
, Others believe that a fault consisting of 1/2 \"high pressure, high temperature liquid line rupture is the most likely design --case scenario.
According to the pipes and valves of the refrigeration system, the leakage rate can be calculated by applying the principle of fluid flow combined with the thermodynamic properties of the heat exchanger.
Seidl and Taylor2005)
Check the leakage of 0. 25 in. (6. 35 mm)hole. Using R-
Temperature and pressure of 22 and 40 [degrees]F(4. 4[degrees]C)and 83 psia (572 kPa)and 100[degrees]F (37. 8[degrees]C)and 210 psia (1448 kPa)
The leakage rate is calculated as 3. 5 lb/min(0. 026 kg/s)and 8. 5 lb/min (0. 064 kg/s), respectively.
The leakage rate is calculated at 34 lbs/min at higher temperatures and pressures (0. 257 kg/s).
They recommend a leak rate of 15 lbs/min (0. 11 kg/s)
Think of similar
The leakage rate of toxic refrigerant is similar to 0. 25 in. (6. 35 mm)
Drilling is not an unreasonable estimate of puncture or accidental drilling.
Refrigerant release is usually a jet stream consisting of steam only, liquid only, or a mixture of steam and liquid (i. e. , two-phases).
The ventilation system is designed to dilute the refrigerant evaporation concentration to the selected value, so the expected refrigerant evaporation leakage rate selected by the designer determines the ventilation rate.
The four variables that affect the steam leakage rate are: the pressure, temperature and State of the refrigerant (Steam or liquid)
, Physical dimensions of holes or holes.
The variables that usually lead to high leakage rates are high pressure, high temperature, large opening and/or liquid release.
Low pressure, low temperature, small holes and/or avapor releases are often characteristic of low leakage rates.
This is not exactly the case in all cases, but it does show the overall trend correctly.
For example, high pressure, high temperature liquid leakage through a large hole will be great.
In contrast, the leakage pressure through the small hole, the low temperature steam will be much smaller.
Liquid under high pressure provides a greater rate of leakage due to high density and greater flow rate through the orifice.
The high temperature liquid also increases the leakage rate due to the high proportion of flash steam generated.
From another point of view, the refrigerant liquid leaks more, so it is more difficult to deal with steam leaks through the same hole, the same pressure and temperature.
Therefore, the maximum amount of steam generated by high pressure, high temperature, liquid leakage (volume)
Therefore, the maximum safety risk is posed within the cabin.
Liquid leakage is possible by combining the following temperatures and pressures: high and high, high and low, low and low.
At high pressure and high temperature, the volume of flash steam is about 20%-
According to the actual pressure and temperature, the leakage mass flow rate accounts for 40% of the total flow rate.
The flashing of the steam causes the liquid to cool down to its thermodynamic equilibrium temperature at atmospheric pressure.
The refrigerant that supplies the leak will also reduce the temperature according to the pressure.
When upstream pressure drops to atmospheric pressure, the rate of leakage through the orifice is almost zero.
However, depending on the location of the leak, the refrigerant may still be present in the source container or pipe.
The liquid that leaves absorbs heat from the surface it touches, thus vaporizing as it cools the surface.
If enough liquid is leaked, it may gather on the floor of the computer room, cooling the floor after producing a large amount of steam, producing only a small amount of steam.
At this point, the heat that evaporates the refrigerated liquid comes only from a small amount of heat that remains in the floor and surrounding air.
If the temperature of the liquid is low, the amount of flash is much less (
In order of quality 10%)
So there is less steam generated.
However, if the pressure is high, the leaking liquid will be replenished quickly, and the liquid that leaves will produce steam to cool the surface on which it is in contact with the machine room.
Low pressure liquids will also produce Flash steam at the same low fraction, but will not be heavily replenished like high pressure liquids.
Assuming that the flow is not blocked, the amount of steam leaking from the orifice depends on the hole size and the upstream pressure.
The upstream temperature affects the leakage rate only by affecting the upstream steam density.
However, if the upstream pressure is greater than the critical pressure (
Depending on the size of the hole)
, The traffic is blocked and does not depend on the upstream pressure.
Under blocked flow conditions, changes in upstream temperature and pressure will affect the flow rate in the same way that affect the upstream steam density.
Liquid jet release.
When the hole causing the release is located at or below the liquid Steam interface, the liquid will exit.
The pressure in the container or pipe generated due to the thermodynamic equilibrium condition pushes the liquid into the hole.
With refrigerant, part of the pressure drop of the liquid jet will flash into avapor.
So this is a twophase flow.
Because the refrigerant usually flashes liquid to steam to a certain extent, pure liquid release is not considered in addition to predicting liquid flow close to the hole or rupture.
The flow of liquid from the container (such as the storage tank) through the hole depends on the pressure difference inside and outside the container and the development of the gravity head
Pushed by the liquid above the hole (AIChE 1996): [E. sub. l]= [c. sub. o][A. sub. h][[rho]. sub. l][[2((p-[p. sub. o])/[[rho]. sub. l])+ 2g[H. sub. l]]. sup. 1/2](1)
The shape of the container also affects the flow rate of the liquid through the hole.
For vertically oriented containers, it can be used (AIChE 1996). [H. sub. l]= 4[V. sub. l]/ [pi][d. sup. 2](2)
When the container is normal, then (AIChE 1996), [H. sub. l]= d/2 (1 -cos[[theta]. sub. l])(3)[V. sub. l]= L[d. sup. 2]/4 ([theta]-
Nature of refrigerant;
Pressure and temperature
Different combinations of these factors will produce different steam release rates.
Below is the low vapor release potential of the combined custom fromhigh as Brown (2005)
: * Release Scenario 1: liquid, high pressure, high temperature * release Scenario 2: gas, high pressure, high temperature * release Scenario 3: liquid, high pressure, low temperature * release Scenario 4: liquid, low pressure, low temperature * release Scenario 5: gas, low pressure, low temperature is the worst
Case realistic scenario and provide background information for selecting the realistic release rate for ventilation chamber design.
Figure 6 shows a schematic diagram of an atypical refrigeration cycle that determines where these release scenarios will occur during this process. [
Figure 6 slightly]
Release Scenario 1: liquid, high pressure, high temperature one liquid, high pressure, high temperature release two-phaseflow.
The pressure in the container or pipe generated due to the thermodynamic equilibrium condition pushes the liquid into the hole.
The sudden pressure drop at the release point causes a part of the liquid jet to flash into the steam.
The remaining liquid pool on the floor of the mechanical chamber at boiling point temperature (Brown, 2005)
After that, it slowly warms up to the ambient temperature.
Therefore, the steam emission rate is calculated in three steps: 1)
Determine the total liquid weight rate in the hole; 2)
The fraction of flash burning liquid is calculated; and 3)
Calculate the rate of evaporation from the surface of the liquid pool.
Several assumptions must be made regarding the release size, release area, release temperature and air speed of the refrigerator.
The size of the liquid refrigerant pool is considered to be the size of the equilibrium pool (
Evaporation rate is limited to no more than the release rate of the liquid minus the discharge rate of the flashing liquid)
The liquidation depth is 0. 394 in. (10 mm)(US EPA 1992).
During the release from the pipe, the liquid expands and cools to the boiling point.
For refrigerants whose boiling point is lower than the environmental conditions, the liquid pool will gradually warm, but it is likely that the ambient temperature will never be reached until it is completely evaporated.
The liquid pool also cools the surrounding air.
Therefore, the pool temperature T2 in equation 13 is considered to be larger in 32 [degrees]F (0[degrees]C)
Or the boiling point temperature of a specific refrigerant.
For those chemicals whose boiling point is lower than 32 [this is a conservative assumption]degrees]F (0[degrees]C)
Because the liquid will stay cooler than [32]degrees]F (0[degrees]C)
For a period of time.
For example, the purpose of the calculation is that the air speed of the overflow is 50 ft/min (0. 254 m/s).
This is equivalent to the 20,000 cfm recommended by Brown (2005)
All mechanical and cross rooms
Section area [400]ft. sup. 2](37. 2[m. sup. 2]).
Lower ventilation rates and smaller room sizes produce similar wind speeds, which are the only important inputs for evaporation calculation.
In order to determine the total steam emission rate, the mass flow rate of the flashing liquid (
Using equal entropy balance)
Added to the evaporation rate.
The potential fault position of the valve lies directly behind the container of liquid high pressure and high temperature refrigerant, such as the defective liquid pipeline valve behind the receiver tank.
Simplified short tube release without wall friction, valve loss factor and gravity head minimizes the necessary assumptions for the heating system.
This release scheme depends only on the diameter of the hole and the pressure difference inside and outside the pipe.
So although this scene is simple, it is still very realistic.
Equation 2 is reduced :[E. sub. l]= [c. sub. o][A. sub. h][[rho]sub. l][[2((p-[p. sub. o])/[p. sub. l])]. sup. 1/2](18)
Emission coefficient recommended by environmental protection bureau [c. sub. o]= 0.
However, this coefficient depends on the flow conditions of the exit hole, and [c. sub. o]
= 1 represents the flow that is not hindered by the shape of the hole (
Like a broken pipe).
During the release process, the pressure and temperature inside the storage container remain constant (US EPA 1992).
In fact, the loss of liquid refrigerant from the valve causes evaporation inside the container, thereby reducing the temperature and pressure of the system.
Therefore, the total liquid emission rate generated over time will be slightly faster than the rate calculated using constant pressure and temperature assumptions, so this is a simpler and more conservative approach.
As mentioned above, the flashing emission rate of R-
The area of 134 is calculated using the equal entropy method.
Liquidation remaining
A pool is formed in 134a.
The size of the swimming pool is related to time, and the air speed is calculated using 50 ft/min (0. 254 m/s).
The rate of the flashing liquid is proportional to the total liquid release rate and decreases slowly over time.
Soon after release, the pool size is small, so the pool evaporation rate is negligible.
However, over time, the pool will continue to grow until the balance is reached, and the amount of liquid refrigerant in the supply pool is equal to the evaporation rate in the equilibrium state, the resulting total steam emission rate is equal to the total liquid emission rate.
The above calculation is repeated for other aperture.
Figure 7 and Figure 8 show the dependence of various calculation rates on the diameter of R-release holes
134a and ammonia, respectively.
The total liquid mass emission rate, the evaporation emission rate caused by flicker, the evaporation rate of the equilibrium liquid pool and the total steam emission rate are in log-
Log scale of two examples: Ammonia (R-717)and1,1,1,2-
Four fluorine (R-134a).
Steam released from the flash and expansion of 0. 25 in. (6. 35 mm)
Holes represent about 95% (
5% will exceed this)
Accidents found in the database. A 0. 5in. (12. 7 mm)
99% of the accidents occurred in this hole.
Release Scenario 2: gas, high pressure, high temperature, which was originally rated as the second worst steam release potential.
There may be high pressure, high temperature gas release in the pipeline between the compressor and the condenser (see Figure 6).
If the pressure in the pipe exceeds the critical pressure, the flow rate is equal to the speed at which the sound passes through the hole and the flow is \"blocked \".
\"If so, the steam discharge rate is constant no matter how much the pressure inside the pipe is larger than the critical pressure.
Therefore, for this case, the situation of suffocation is invalid.
In this case, emissions are much lower than observed (see Table 3. 2)
It will not be considered as a reasonable basis for the ventilation rate of the room.
Release Scenario 3: liquid, high pressure, low temperature. This scene is very similar to the scene 1 described.
There may be high pressure, low temperature liquid refrigerant release between the heat exchanger and the expansion valve.
All the equations used in scenario 1 can also be applied to this scenario.
The emission rates generated in this scenario are not expected to differ significantly compared to Scenario 1, as the total liquid emission rate is only driven by the differential pressure difference inside and outside the container.
The lower the temperature of the refrigerant, the lower the flashing rate and evaporation rate.
However, once the system is balanced (i. e.
Evaporation rate equals total liquid emission rate minus flashing rate)
The temperature difference between the two scenarios will not have any effect, and this scenario will provide the same emission rate as scenario 1. [
Figure 7 Slightly][
Figure 8:
Release Scenario 4: low pressure, low pressure, low temperature expansion valve and evaporator may have low pressure, low temperature liquid release of refrigerant.
If the pressure in the pipe or container is lower than the ambient pressure, the release is controlled by the weight of the liquid above the orifice and will not be released until the pressure is equal.
Due to the low temperature compared to Scene 1, the rate of flashing liquid is significantly reduced.
Due to the low overall liquid emission rate, the balance pool size is less than scenario 1.
Since the calculation rate is significantly lower than Scenario 1, it is also excluded to use this scenario when determining the ventilation rate.
Release Scenario 5: gas, low pressure, low temperature this scenario is very similar to Scenario 2.
There may be low pressure, low temperature gas refrigerant release between the evaporator and the compressor.
All equations used in scenario 2 can also be applied to this scenario.
The resulting steam emission rate is expected to be lower than the steam emission rate calculated in scenario 2, as the total steam emission rate is driven only by the differential pressure difference inside and outside the container.
This decrease in the differential pressure will lead to a decrease in the emission rate.
If the pressure in the pipe or container is lower than the critical pressure, the situation of blocking flow no longer exists, so the steam flow rate depends on the pressure in the container or pipe.
Total Quality flow of the United Nations
Blocking flow is less than blocking flow.
Since the calculated emission rate is significantly lower than Scenario 1, this scenario will also be excluded when determining the ventilation rate.
Recommended release scenario for ventilation room design to consider possible worst case scenario
In the case, it is recommended to use high temperature and high pressure release.
Although two people
Phase release is the most realistic, taking into account all the variables of the evaporation pool, including surface velocity, pool depth, pool size (floor area)
The consideration of heat transfer becomes very difficult and full of vague assumptions.
In addition, the emission rate of the evaporation pool may become very large.
Therefore, it is assumed that a drain pipe is provided to capture any liquid that will accumulate.
All steam emissions will be generated by flashing steam starting from 0. 5 in. (12. 7 mm)hole.
Only consider flash steam (
Potential liquid does not evaporate)
For ammonia, this is an accident scenario with a probability of only over 5%, which seems to be a reasonable probability for the design (
Including evaporation, this scenario produces a probability of more than 1%).
It is further assumed that similar probability will occur for other refrigerants.
The purpose of ventilation rate ventilation room is to dilute the indoor air and make the recommended concentration limit (RCL)
In Tables 1 and 2 of ANSI/ASHRAE standards 34 (ASHRAE 2010)
No more.
However, depending on the actual leakage rate, ventilation may or may not, dilute the refrigerant concentration to RCL or lower using the current standard 15 method.
This section will introduce methods in which adesigner can specify a ventilation rate to ensure that the concentration is below the RCL value.
In subsequent paragraphs, the derivation of the equation required to estimate the concentration of the machine room due to accidental release of any refrigerant is given.
Detector activation of ventilation system standard 15 (ASHRAE 2010)
An overview of the requirements that each refrigeration room contains a detector that activates alarms and mechanical ventilation in the event of a refrigerant leak.
The alarm is activated at a refrigerant concentration level not higher than the threshold value (TLV)
Time weighted average (TWA).
Threshold limit value-time-weighted-average (TLV-TWA)
Average concentration of exposure during normal working days (
40 hours a week, 8 hours a day)
No adverse effects.
TLV-is listed in Table 3-
TWA of different vegetables.
In the analysis and example below, TLV-
TWA will be used as thresh-
It is old for the activation of ventilation.
For those TLV-
TWA is not available and 10% of RCL is used as a detector threshold.
The refrigerant concentration mass balance equation in the room is used to solve the concentration in the room, which is a function of the source and loss of pollutants, mainly ventilation.
Several assumptions were made in derivation and resolution of this mass balance: 1.
Good room-mixed.
When the pollutant refrigerant is released into a closed room and becomes a gas, the quality of the discharge is diluted instantly in the volume of the room.
There are not many complicated tools to explain density, mixing rate and other parameters to block-
This assumption would underestimate the concentration of some rooms and overestimate the concentration of other rooms.
For example, if the refrigerant is initially smaller than the air and ventilation rate (lowmixing)
, The concentration on the floor will be higher, and the concentration near the ceiling will be lower.
As a result, many emergency exhaust outlets are located closer to the ground.
Once the ventilation rate increases, a better mix is likely to occur. 2.
Pollutants are inert.
There is no reaction in the volume of the room, whether it is homogeneous or heterogeneous. 3.
No cores or condensation.
Once the pollutant becomes a gas, there will be no nuclear or condensation.
For space volume V, the change in concentration C is equal to the emission rate of the room pollutant E minus the ventilation Q: V dC (t)
This will also cause omissions.
We acknowledge that better reporting and more data representing the leakage of fluorine-carbon refrigerant will improve understanding of the issue, but the data are useless --
Able to use through public and public sources.
Although most of the data from actual emissions are ammonia, trends in potential leak locations and causes may be studied.
In addition, for the worst case scenario, the threshold probability of emissions exceeding can be estimated
Emission scenarios.
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Peter is aprincipal and vice president, Anko byyer-
Lout is a project of scientist CPP.
At Fort Collins, CO.
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