Blower control system

1. A controller for a sub slab exhaust system,

said controller comprising an input device adapted to receive one or more input signals from one or more pressure sensors each adapted to measure a pressure drop at a location below a sub slab of a first building relative to a pressure above said sub slab; an output device adapted to produce an output signal to control a speed of a blower adapted to exhaust air below said sub slab; a microprocessor programmed to perform calculations based on said one or more input signals to control said output signal; and a permanent memory comprising computer readable instructions to cause said microprocessor to carry out at least the steps of:

i) at the beginning of a first control cycle period, measure said one or more pressure drops indicated by said one or more input signals from said one or more pressure sensors;

ii) determine the ratio of each of said measured pressure drops to a desired pressure drops for each of said pressure sensors;

iii) determine the minimum of said pressure drop ratios and either:

1) output by said output device, an output signal adapted to increase said blower speed by a first fractional increase if said minimum of said pressure drop ratios is between a first amount and 1 wherein said first amount is less than 1;

2) output by said output device, an output signal adapted to increase said blower speed by a second fractional increase if said minimum of said pressure drop ratios is less than said first amount; or

3) output by said output device, an output signal adapted to decrease said blower speed by a first fractional decrease if said minimum of said pressure drop ratios is greater than or equal to 1; and

iv) execute steps i), ii) and iii) at the beginning of a second control cycle period.

2. The controller of claim 1 wherein said first fractional increase is about 1% and said first control cycle period is about 1 second.

3. The controller of claim 1 wherein each of said desired pressure drops for each of said pressure sensors is 0.01 inch WC or greater.

4. The controller of claim 1 wherein said second fractional increase is about 5% and said first amount is about 0.95.

5. The controller of claim 1 wherein said first fractional increase is zero and said second fractional increase is greater than zero.

6. The controller of claim 1 wherein said steps comprise:

a) output by said output device, an output signal adapted to increase said blower speed by a third fractional increase if said minimum of said pressure drop ratios is less than a second amount wherein said second amount is less than said first amount.

7. The controller of claim 6 wherein said third fractional increase is about 10% and said second amount is about 0.85.

8. The controller of claim 1 wherein said first fractional increase is more than said first fractional decrease.

9. The controller of claim 1 which further comprises an internet communication system for receiving remote instructions to control said microprocessor and transmitting compliance data from said microprocessor.

10. The controller of claim 1 wherein said input device is adapted to receive said input signals from three or more pressure sensors.

11. The controller of claim 1 wherein said first control cycle period is less than about 10% of the time it takes the pressure in said first building to respond to a sudden change in building configuration.

12. The controller of claim 11 wherein said sudden change in building configuration is an exterior door opening.

13. A controller for a sub slab exhaust system,

said controller comprising an input device adapted to receive one or more input signals from one or more sensors measuring one or more indications of adequate air flow from a first building out through a sub slab of said first building; an output device adapted to produce an output signal to control a speed of a blower adapted to exhaust air from below a sub slab of a first building; a microprocessor for performing calculations based on said one or more input signals to control said output signal; and a permanent memory comprising instructions to cause said microprocessor to carry out at least the steps of:

i) at the beginning of a first control cycle period, measure said one or more indications of adequate air flow according to said one or more input signals from said one or more sensors;

ii) determine the ratio each of said measured indications to a desired indication for each of said sensors;

iii) determine the minimum of said measured ratios and either:

1) output by said output device, an output signal adapted to increase said blower speed by a first fractional increase if said minimum of said measured ratios is between a first amount and 1 wherein said first amount is less than 1;

2) output by said output device, an output signal adapted to increase said blower speed by a second fractional increase if said minimum of said measured ratios is less than said first amount; or

3) output by said output device, an output signal adapted to decrease said blower speed by a first fractional decrease if said minimum of said measured ratios is greater than or equal to 1; and

iv) execute steps i), ii) and iii) during a second control cycle period.

14. The controller of claim 13 wherein said one or more indications are inversely related to said air flow through said sub slab and wherein said ratios are computed by dividing said desired indications by said measured indications.

15. The controller of claim 14 wherein said one or more indications comprise a contaminant level in said first building, said contaminant being a vapor originating below said sub slab.

16. The controller of claim 13 wherein said one or more indications comprise a flow rate in said duct.

17. The controller of claim 13 wherein said one or more indications comprise a pressure in said duct relative to a pressure in said building.