Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
  • F24F11/00—Control or safety arrangements
  • F24F11/30—Control or safety arrangements for purposes related to the operation of the system, e.g. for safety or monitoring
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
  • F24F2110/00—Control inputs relating to air properties

Definitions

• Ventilation measurement in its most general form implies measuring the supply rate of ambient air to a building and how this air is distributed within the building space.
• Field measurement of ventilation can be performed with several known techniques. The most commonly used technique involves measuring the air flow rates in the ventilation equipment, ducts or supply- and exhaust devices. Such ventilation measurements can only be used in mechanically ventilated buildings. The methods also have some additional limitations:
• ventilated system involves all spaces, that are somehow connected in a ventilation sense, i. e. all spaces to which or from which air can be transferred from or to other parts of the system.
• the only air which can be supplied over the boundary of a ventilated system is ambient air.
• a tracer gas is mixed into all spaces of the ventilated system to the same initial tracer concentration, after which the decay as a function of time is registered in one or several points.
• Different ventilation parameters can be calculated from the decay course. Some different cases can be separated.
• tracer gas is mixed to an even concentration in the whole of the ventilated system, but during the measurement of the decay, no effort is done to influence the mixing in the system.
• different decay curves are usually obtained in different parts of the system, which reflects the different distribution of ventilation air.
• Well ventilated parts of the space shows a quicker decay than badly ventilated parts.
• the evaluation is done by measuring the area under the plot of concentration versus time from the beginning of the decay until all tracer gas has disappeared from the system. This area (integral) constitutes a direct measure of the mean age of air at the measuring point.
• the local mean age of air tells how long the air around the measuring point in average has stayed in the building, since it entered as ambient air.
• By measuring the decay at several positions in the system it is possible to map the distribution of ventilation air. Spaces mainly ventilated with direct supply of outside air, show a shorter mean age than such mainly ventilated with air from other spaces.
• the local mean age in the exhaust air is always equal to the inverted value of the specific ventilation flow rate.
• tracer gas is injected into the system with a constant rate. After some time the concentration of tracer gas and its distribution in the system will attain a steady state. Also in this case some special cases can be distinguished.
• the whole system shall be mixed by means of fans, so that the tracer gas concentration is equal everywhere.
• the evaluation is performed by measuring the steady state concentration and from that value calculate the total ventilation flow rate as the quotient between the rate of tracer gas emission and the tracer gas concentration.
• tracer gas is spread with a constant rate, but the emission is to be evenly (homogeneously) distributed in the whole space of the system.
• This technique (the homogeneous emission technique) is relatively new and is practically performed by dividing the system space in smaller zones, in each of which tracer gas is emitted with a rate, which is proportional to the volume of the zone.
• the specific ventilation rate of the system can be calculated from the inverted value of the mean age of air at that point.
• This technique can be used in a zone-divided system and implies that an automatic dosing device injects tracer gas to the different zones, in a way that all zones achieve the same tracer gas concentration.
• the technique requires a relatively complicated equipment, with feedback between the measured tracer gas concentration and the injection rate. The direct supply of ambient air to each zone can be estimated in this way.
• the method which this invention refers to, is meant to facilitate ventilation measurement with tracer gas in field work. I will therefore shortly describe the problems of applying the different known techniques in field work and demonstrate how the new invention can solve these problems.
• the air mixing constitutes a special problem with method 1a and 2a. Artificial mixing is impractical in occupied premises.
• This passive tracer gas technique has many advantages for field measurements. It yields among other things the average ventilation performance during an extended time of normal occupancy. This technique can however occasionally be less desired. One such occasion is when a short term measurement is desired, for example during a working day, due to the fact that the ventilation may be decreased during off-work time. Another occasion is when it is desirable to have the ventilation measurement rapidly and non-expensively concluded, for example for a routine check of the ventilation performance, in which case it is allowed to accept a value, which is less representative for an extended time period.
• the air sampling shall namely be performed during "steady state conditions". If the air has a mean age of 2 hours or more (which is normal in dwellings), it is a delay of 8-10 hours to approach this state after positioning the tracer gas sources. When measuring extended times, this build up period can be neglected, but with short term measurement it is of essential importance. The samplers must not be opened before a considerable time period has elapsed, which complicates the handling.
• the invention solves these problems.
• the integrating samplers are active already from the beginning of the tracer gas emission, the spreading of tracer gas in the different zones may be performed in any pace, which is convenient. Any time delay between the injections into the different zones is without importance.
• the integrating samplers should have the characteristics, that their rate of tracer gas sampling is directly proportional to the concentration of trace gas in the air. This is essentially true for samplers of the diffusive type and for all "pumped" sampling.
• samplers After the sampling the samplers are inactivated and sent to a laboratory for analysis of the amount of sampled tracer gas (M).
• the integral can be evaluated, from which the local mean age of air ⁇ can be calculated where m/V is the amount of injected tracer gas per volume unit of the space.
• zone used above and in the claim may be equivalent to a "room” in premises or dwellings but must not be so.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Sampling And Sample Adjustment (AREA)

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• 1996
  • 1996-07-29 SE SE9602884A patent/SE510876C2/sv not_active Application Discontinuation
• 1997
  • 1997-07-28 DE DE69709120T patent/DE69709120D1/de not_active Expired - Lifetime
  • 1997-07-28 AU AU37151/97A patent/AU3715197A/en not_active Abandoned
  • 1997-07-28 EP EP97933981A patent/EP0917635B1/en not_active Expired - Lifetime
  • 1997-07-28 WO PCT/SE1997/001315 patent/WO1998004872A1/en active IP Right Grant

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