Dynamic control of dilution ventilation in one-pass, critical environments

Abstract

A dilution ventilation control system for use in a one-pass, critical environments comprising: one or more one-pass, critical environments comprising, a variable source of supply airflow volume, an exhaust for completely exhausting the airflow volume supply from the critical environment and from a building comprising the critical environment through one or more exhaust ducts; and at least one an airflow control device provided in one or more of the ducts to vary the exhaust airflow volume from the critical environment; a facility monitoring system comprising at least one air contaminant sensor for sensing at least one air contaminant of the critical environment; a signal processing controller that generates one or more airflow command signals based at least in part on at least one sensed air contaminant; and a critical environment airflow controller that uses the airflow command signal to at least partially control the critical environment's supply and exhaust airflow volumes.

Description

CROSS-REFERENCE [0001] This is a continuation-in-part of U.S. Provisional Patent Application Ser. No 60 / 660,245 filed on Mar. 10, 2005.FIELD OF THE INVENTION [0002] This invention relates to systems for controlling ventilation to dilute contaminants within critical environments or spaces such as laboratories and vivariums which utilize a “one-pass” ventilation strategy in which the airflow out of each environment is entirely exhausted without a recirculated air component, and more particularly, to systems and methods for varying the flows of supply and exhaust air into and from these environments for the purposes of controlling the dilution of air contaminants based on changes in the presence of these contaminants as sensed by a facility monitoring system. BACKGROUND OF THE INVENTION [0003] This invention relates to the dynamic control of dilution ventilation in one-pass, critical environments. Critical environments in the context of this invention relate to spaces, areas or rooms i...

AI Technical Summary

Benefits of technology

[0024] The air in modern laboratories is often quite clean such that high air change rates are unnecessary except for example when a spill happens; poor lab practices generate fumes, vapors or contaminants in the lab outside the containment devices like fume hoods; or when the containment devices work poorly leaking chemical fumes into the space. Since the far majority of the time the lab air is clean, the dilution ventilation airflow can be brought down significantly the majority of the time to a level such as 2 to 4 ACH's vs 6 to 12 ACH's creating significant ventilation savings. Additionally when a spill occurs, the system can increase the dilution ventilation rate to a high level such as 12 to 15 ACH, providing increased safety through a fast evacuation of the spilled vapors from the lab.

[0025] Dynamic control of dilution ventilation based on monitoring the quality of air with a facility monitoring system can be accomplished with several different embodiments. Perhaps the simplest approach to dynamically vary air change requirements in one-pass, critical environments, such as labs or vivariums, would be to use a single, broad based contaminant sensor such as a TVOC or total volatile organic compound sensor located in each room or airflow control zone that is to be controlled. This approach can for example increase the dilution ventilation airflow requirements when the contaminant sensor detects that contaminants are above a given threshold level. When the contaminant level returns below the given threshold level, the dilution ventilation airflow requirement is brought back down to the minimum set point level. In all conditions if the thermal load or special exhaust make-up airflow requirements are above the required dilution ventilation flow requirements, then these requirements will override and take control of the room's airflow level in a high select form of control.

[0038] To prevent multiple spaces from going to high dilution ventilation incorrectly due to a high outdoor level of contaminants, another embodiment of the current invention describes a means to vary the dilution ventilation of a space not on the absolute value of a given contaminant, but instead on the differential value of that air contaminant vs. either an outdoor air value, a supply airflow value, or the value measured in an adjacent or nearby space. In this manner the room does not incorrectly increase the flow of a contaminated supply air stream, when the contaminant sensed is not from inside the room. In a related embodiment, if the absolute level of the room exceeds the threshold value for action, yet the source of the contaminant is from the supply of outside air, the supply air may be decreased. For example, the supply air may be decreased by commanding a lower dilution ventilation level and / or commanding an increased temperature set-point, to reduce the thermal load requirements on the supply volume.

Problems solved by technology

In particular, the exposure of these people to animal allergens, such as rat urine protein (RUP) or mice urine protein (MUP), that is often carried in the air on particulates can over time sensitize the animal care workers and researchers, and create allergic reactions in these individuals from the animals via contaminated air in the facility.

Accordingly, the minimum fixed air changes requirements for 100% outside air in conventional laboratory, vivarium, or other dilution ventilation systems often results in wasted resources (i.e., fresh outdoor air) and unnecessarily excessive operating costs as well as high up front capital costs for sufficient sizing of the building's heating, ventilating and air conditioning system also referred to as the HVAC system.

First, the numbers of laboratory fume hoods and related special exhaust devices has decreased.

Although in the early 90's the amount of lab instrumentation increased significantly, over time this equipment has become smaller and more energy efficient.

Although this approach can save energy it has several safety problems that negate its prudent use.

For example, a spill or release of hazardous vapors can occur during an unoccupied time increasing the level of contaminants in the air above safe levels.

If someone were to walk into the space during this scheduled unoccupied time, they could be injured by the higher level of contaminants in the air.

Furthermore, occupancy detectors can have problems with detecting people in a broken up space with many barriers such as lab shelves and equipment between the sensor and the occupants.

They also need to constantly see motion to operate and may fail to see someone quietly reading with insufficient motion to trigger the higher safe airflow.

Images