Ventilator cycle

Once one understands the primary control mechanism of a ventilator, one can examine how a ventilator starts, sustains, and stops inspiration and what it does between inspirations. A ventilator cycle can be broken down into four phases ... 

In pressure ventilation, most ventilators cycle from inspiration to expiration when inspiratory flow decreases to a predetermined percent of its peak flow or when a preset inspiratory time is reached. It has become increasingly clear that cycling plays an important role in assuring patient-ventilator synchrony (11). This has been quite well studied in pressure support ventilation and several authors have shown that a fixed cycle value can lead to premature cycling in patients with restrictive diseases and delayed cycling in those with obstructive disease (12,13). 

Equipment operating schedules Confirm that the timing of occupied and unoccupied cycles is compatible with actual occupied periods, and that the building is flushed by the ventilation system before occupants arrive. ASHRAE 62-1989 provides guidance on lead and lag times for HVAC equipment. In hot, humid climates, ventilation may be needed during long unoccupied periods to prevent mold grow th. 

It will be critical to update publications such as the Design Guide Book in the industrial ventilation field on a regular basis. Never stop the developing process study, develop, and update everything, taking into account life-cycle ecological issues. 

Define target levels for the ventilation system, such as reliability, energy consumption, investment, life cycle costs, etc. 

Several tools can be used to evaluate the environmental consequences of an industrial ventilation project. Some of the most common methods used are covered in this chapter. The life cycle assessment tool is considered in detail, as it is a comprehensive and product-oriented approach that is covered by international standardization. Other tools, such as risk assessment, cost-benefit... 

The subject of the study can be either a single energy-using device, such as a pump, or an entire ventilation system with all its components. A study focuses on the life cycle of the system or device, and normally is a comparison of two or more alternatives. The goal is to find the most economical solution on the basis of the total costs (investment and operation). 

Considering the energy and maintenance costs during the life cycle, the cheapest investment is not always the best. It may, for instance, be profitable to buy a ventilation unit with a heat recovery system, which may increase the unit investment by 50%. The return on the investment in such a case may be in excess of 20%. 

In ventilation design, these calculations are used routinely for equipment comparison. Plans are, however, to include life cycle cost calculations in the terms-of-tender contract. 

LCC calculations frequently provide energy-efficient solutions. This gives reduced energy consumption and a reduction in environmental pollution. For example, the installation of a heat recovery system in a ventilation system may reduce the energy consumption and emissions by 50 to 80%. Figure 16.1 compares life cycle cost and life cycle assessment calculations. 

FIGURE 16.5 Comparison of different ventilation unit combinations. The life cycle Is 20 years and the interest rate is A%. In sensitivity analysis the variation of the Interest rate did not change the order of different combinations signlBcantly. 

Min GR, Edwards RL, Taylor FW, Recy J, Gallup CD, Beck JW (1995) Annual cycles of U/Ca in corals and U/Ca thermometry. Geochim Cosmochim Acta. 59 2025-2042 Moore WS (1981) The thorium isotope content of ocean water. Earth Planet Sci Lett 53 419-426 Moran SB, Hoff JA, Edwards RL, Landing WM (1997) Distribution of Th-230 in the Laborador Sea and its relation to ventilation. Earth Planet Sci Lett 150 151-160 Muhs DR, Simmons KR, Steinke B (2002) Timing and warmth of the Last Interglacial period new U-series evidence from Hawaii and Bermuda and a new fossil compilation for North America. Qrrat Sci Rev 21 1355-1383... 

PAOP This must be lower than the PA diastolic pressure to ensure forward flow. It is drawn as an undulating waveform similar to the CVP trace. The normal value is 6-12 mmHg. The values vary with the respiratory cycle and are read at the end of expiration. In spontaneously ventilating patients, this will be the highest reading and in mechanically ventilated patients, it will be the lowest. The PAOP is found at an insertion length of around 45 cm. 

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