Systems and methods for whole-house dehumidification based on dew point measurements

• US 7,574,871 B2
• Filed: 10/27/2004
• Issued: 08/18/2009
• Est. Priority Date: 10/27/2004
• Status: Active Grant

• Current Assignee: Research Products Corporation
• Original Assignee: Research Products Corporation
• Inventors: Bloemer, John M., Higgins, Timothy E.
• Primary Examiner(s): JIANG, CHEN WEN
• Application Number:
  US10/974,319
• Publication Number:
  US 20060086112A1
• Time in Patent Office: 1,756 Days
• Field of Search: 621/766, 621/761, 62/93, 236/44.R, 236/44.C, 236/44.A, 165/222, 165/229, 165/230
• US Class Current: 62/176.6
• CPC Class Codes: F24F 11/0008 for air-humidification F24F11/30 takes precedence
• CPC Class Codes: F24F 11/30 for purposes related to the operation of the system, e.g. for safety or monitoring
• CPC Class Codes: F24F 11/62 characterised by the type of control or by internal processing, e.g. using fuzzy logic, adaptive control or estimation of values
• CPC Class Codes: F24F 2110/20 Humidity
• CPC Class Codes: F24F 3/153 with subsequent heating, i.e. with the air, given the required humidity in the central station, passing a heating element to achieve the required temperature
• CPC Class Codes: G05D 22/02 characterised by the use of electric means

Abstract

A dehumidifier system is connected to an interior space of a building through supply and return ducts, either directly and/or through an HVAC system. Controllable dampers can be used to select how the dehumidifier system is connected to the interior space and the HVAC system. The dehumidifier determines the dew point of the ambient air from temperature and relative humidity measurements taken at location(s) of relative humidity and temperature sensors. Based on the determined dew point, the dehumidifier system determines whether to operate. The temperature and relative humidity sensors can be located in the interior space or within the dehumidifier, where they project into the air stream flowing through the dehumidifier. The dehumidifier system operates in response in part to blower calls to the HVAC system and controls the HVAC system and a ventilation system to distribute the dehumidified air and outside air throughout the building.

Claims

1. A method for automatically dehumidifying at least one interior space of a structure using a dehumidifier at least indirectly connected to the at least one interior space by at least one dehumidifier return duct and at least one dehumidifier supply duct, the structure having an HVAC system that has at least an HVAC blower and that is connected to at least the at least one interior space through at least one of at least an HVAC supply duct and at least an HVAC return duct, the HVAC blower turned on by the HVAC system in response to blower call signals, the dehumidifier associated with the HVAC system and comprising a housing connected to the dehumidifier return and supply ducts and a compressor, a dehumidifier blower, a temperature sensor and a relative humidity sensor contained within the housing, the method comprising:

determining if a measurement event has occurred; and

if a measurement event has occurred;

determining if the HVAC system is in a blower mode;

if the HVAC system is in the blower mode;

determining if the HVAC blower is on; and

if the HVAC blower is not on;

turning the HVAC blower on;

measuring a temperature and a relative humidity of an ambient atmosphere within the housing using the temperature sensor and the relative humidity sensor,

determining a dew point temperature for the interior space based on the measured temperature and relative humidity;

determining if the determined dew point temperature is above a predetermined dew point temperature; and

if the determined dew point temperature is above the predetermined dew point temperature

turning on a compressor of the dehumidifier,

if a blower of the dehumidifier is not on, turning on the blower of the dehumidifier,

drawing air to be dehumidified from at least the at least one interior space through at least the at least one dehumidifier return duct;

dehumidifying the drawn air; and

returning the dehumidified air to at least the at least one interior space through at least the at least one dehumidifier supply duct.

2. The method of claim 1, wherein determining if a measurement event has occurred comprises determining if the predetermined dew point temperature has been changed by at least a predetermined amount.

3. The method of claim 2, wherein:

the dehumidifier has a device usable to select the predetermined dew point temperature; and

changing the predetermined dew point temperature by at least the predetermined amount comprises operating the device by at least an amount that corresponds to the predetermined amount.

4. The method of claim 1, wherein:

determining if a measurement event has occurred comprises determining if a blower call signal has been output.

5. The method of claim 4, wherein:

the dehumidifier has a current air cycle interval; and

determining if a blower call signal has been output comprises determining if the output blower call signal is a first blower call signal of the current air cycle interval.

6. The method of claim 5, wherein determining if a measurement event has occurred further comprises determining that a measurement event has occurred only if the output blower call signal is the first blower call signal of the current air cycle interval.

7. The method of claim 1, wherein:

the dehumidifier has a current air cycle interval; and

determining if a measurement event has occurred comprises determining if the current air cycle interval is within a first predefined interval before the end of the current air cycle interval.

8. The method of claim 7, wherein:

the dehumidifier is associated with an HVAC system that has at least an HVAC blower and that is connected to at least the at least one interior space through at least one of at least an HVAC supply duct and at least an HVAC return duct, the HVAC blower turned on by the HVAC system in response to blower call signals; and

determining if a measurement event has occurred further comprises determining that a measurement event has occurred only if the current air cycle interval is within the first predefined interval before the end of the current air cycle interval and no blower call signals have been received during the current air cycle interval.

9. The method of claim 1, wherein:

the temperature and relative humidity sensors are located within the housing such that the temperature and relative humidity sensors are within an air stream of air to be dehumidified supplied to the housing from the at least one return duct; and

measuring the temperature and relative humidity of the ambient atmosphere within the housing comprises measuring the temperature and relative humidity of the air to be dehumidified supplied to the housing from the at least one return duct.

10. The method of claim 1, wherein:

the dehumidifier is located outside of the at least one interior space to be dehumidified such that the temperature and relative humidity sensors are outside of the at least one interior space; and

measuring the temperature and relative humidity of the ambient atmosphere within the housing comprises measuring the temperature and relative humidity of air outside of the at least one interior space to be dehumidified.

11. The method of claim 1, further comprising, prior to measuring the temperature and relative humidity:

turning on the dehumidifier blower; and

waiting at least a first predefined period before measuring the temperature and relative humidity.

12. The method of claim 11, further comprising, prior to measuring the temperature and relative humidity, ensuring the HVAC blower is on.

13. The method of claim 1, wherein:

the at least one dehumidifier return duct and the at least one dehumidifier supply duct comprise;

at least one of;

a common dehumidifier supply duct portion connected to the dehumidifier, at least one dehumidifier supply duct connected directly to the at least one interior space and to the common dehumidifier supply duct portion and at least one dehumidifier supply duct connected to the HVAC supply duct and to the common dehumidifier supply duct portion, and

a common dehumidifier return duct portion connected to the dehumidifier, at least one dehumidifier return duct connected directly to the at least one interior space and to the common dehumidifier return duct portion and at least one dehumidifier return duct connected to the HVAC return duct and to the common dehumidifier return duct portion; and

at least one controllable damper located within at least one of the at least one dehumidifier return duct and the at least one dehumidifier supply duct; and

the method further comprises;

if the HVAC blower is turned on, operating the at least one controllable damper to connect the dehumidifier to at least the HVAC supply duct through at least the at least one dehumidifier supply duct; and

if the HVAC blower is not turned on, operating the at least one controllable damper to connect the dehumidifier to at least the at least one interior space through at least the at least one dehumidifier supply duct.

14. The method of claim 13, further comprising:

if the HVAC blower is turned on, operating the at least one controllable damper to connect the dehumidifier to the HVAC supply duct through at least the at least one dehumidifier supply duct and to the HVAC return duct through at least the at least one dehumidifier return duct and to disconnect the dehumidifier from the at least one interior space,

if the HVAC blower is not turned on, operating the at least one controllable damper to connect the dehumidifier to the at least one interior space through at least the at least one dehumidifier supply duct and to the at least one interior space through at least the at least one dehumidifier return duct and to disconnect the dehumidifier from the HVAC supply duct and from the HVAC return duct.

15. The method of claim 1, further comprising:

determining if the compressor has run for at least a first predefined period; and

if the compressor has not run for at least the first predefined period, continuing to run the compressor.

16. The method of claim 15, further comprising, if the compressor has run for at least the first predefined period:

measuring a second temperature at least near a set of cooling coils connected to the compressor;

determining if the measured second temperature is less than a first predefined temperature; and

if the measured second temperature is not less than the first predefined temperature;

measuring the temperature of the ambient atmosphere around the temperature sensor,

measuring the relative humidity of the ambient atmosphere around the relative humidity sensor,

determining the dew point temperature for the interior space based on the measured temperature and relative humidity,

determining if the determined dew point temperature is above the predetermined dew point temperature, and

if the determined dew point temperature is above the predetermined dew point temperature, continuing to run the compressor.

17. The method of claim 16, further comprising, if the determined dew point temperature is at least equal to the predetermined dew point temperature, turning off the dehumidifier blower and compressor.

18. The method of claim 17, further comprising, if the determined dew point temperature is at least equal to the predetermined dew point temperature, turning off the HVAG blower.

19. The method of claim 18, wherein:

the at least one dehumidifier return duct and the at least one dehumidifier supply duct comprise;

at least one of;

a common dehumidifier supply duct portion connected to the dehumidifier, at least one dehumidifier supply duct connected directly to the at least one interior space and to the common dehumidifier supply duct portion and at least one dehumidifier supply duct connected to the HVAC supply duct and to the common dehumidifier supply duct portion, and

a common dehumidifier return duct portion connected to the dehumidifier, at least one dehumidifier return duct connected directly to the at least one interior space and to the common dehumidifier return duct portion and at least one dehumidifier return duct connected to the HVAC return duct and to the common dehumidifier return duct portion; and

at least one controllable damper located within at least one of the at least one dehumidifier return duct and the at least one dehumidifier supply duct; and

the method further comprising, if the determined dew point temperature is at least equal to the predetermined dew point temperature, operating the at least one controllable damper to return the at least one controllable damper to a state each at least one controllable damper was in prior to the measurement event occurring.

20. The method of claim 17, further comprising:

determining if a second predetermined period has elapsed since the dehumidifier compressor was turned off; and

if the second predetermined period has not elapsed, waiting for the second predetermined time to elapse.

21. The method of claim 20, further comprising, if the second predetermined time period has elapsed:

determining if a current air cycle time interval of the dehumidifier, which the dehumidifier was in when the measurement event occurred, has elapsed; and

if that current air cycle time interval has elapsed, determining if a new measurement event has occurred.

22. The method of claim 21, further comprising, if that current air cycle time has not elapsed:

determining if the predetermined dew point temperature has been changed by at least a predetermined amount; and

if the predetermined dew point temperature has been changed by at least the predetermined amount, determining that a new measurement event has occurred.

23. The method of claim 22, further comprising, if the predetermined dew point temperature has not been changed by at least the predetermined amount, repeating the second predetermined period elapse determination step.

24. The method of claim 16, further comprising, if the measured second temperature is less than the first predefined temperature:

measuring a second time period since the measured second temperature was determined to be less than the first predefined temperature;

determining if the second time period is at least equal to a second predetermined time period; and

if the second time period is at least equal to the second predetermined time period;

turning off the compressor, and

waiting for a third predefined time period to elapse.

25. The method of claim 24, further comprising, after the third predefined time period has elapsed:

measuring the second temperature at least near the set of cooling coils connected to the compressor;

determining if the measured second temperature at least a second predefined temperature; and

if the measured second temperature is not at least the second predefined temperature, repeating these steps until the second temperature is at least the second predefined temperature.

26. The method of claim 1, wherein the structure is a residential, office or light commercial structure.

27. A method for automatically dehumidifying at least one interior space of a structure using a dehumidifier at least indirectly connected to the at least one interior space by at least one dehumidifier return duct and at least one dehumidifier supply duct, the dehumidifier comprising a housing connected to the dehumidifier return and supply ducts and a compressor, a dehumidifier blower, a temperature sensor and a relative humidity sensor associated with the housing, the method comprising:

determining is a measurement event has occurred; and

if a measurement event has occurred;

determining, prior to measuring a temperature and a relative humidity, if an air conditioning call has been made or completed within a first predetermined time;

if an air conditioning call has been made or completed within a first predetermined time, waiting until no conditioning call has been made or completed within the first predetermined time before measuring the temperature and relative humidity;

measuring, subsequent to at least the determining step, the temperature and the relative humidity of an ambient atmosphere within the housing using the temperature sensor and the relative humidity sensor;

determining a dew point temperature for the interior space based on the measured temperature and relative humidity;

determining if the determined dew point temperature is above a predetermined dew point temperature; and

if the determined dew point temperature is above the predetermined dew point temperature;

turning on the compressor of the dehumidifier,

if the blower if the dehumidifier is not on, turning on the blower of the dehumidifier,

drawing air to be dehumidified from at least the at least one interior space through at least the at least one dehumidifier return duct;

dehumidifying the drawn air; and

returning the dehumidified air to at least the at least one interior space through at least the at least one dehumidifier supply duct.

28. A method for automatically dehumidifying at least one interior space of a structure, the structure having an HVAC system that includes an HVAC return duct, an HVAC supply duct, an HVAC blower and at least one HVAC control device that outputs blower call signals, the HVAC blower turned on by the HVAC system in response to the blower call signals, using a dehumidifier connected to the at least one interior space by at least the HVAC system, the dehumidifier comprising a housing and a compressor, a blower, a temperature sensor and a relative humidity sensor located within the housing, the method comprising:

determining if a measurement event has occurred; and

if a measurement event has occurred;

turning on the blower of the dehumidifier;

turning on the HVAC blower if it is not already on;

waiting for a first predefined period;

measuring a temperature of an ambient atmosphere within the housing using the temperature sensor after the first predefined period has elapsed;

measuring a relative humidity of an ambient atmosphere within the housing using the relative humidity sensor after the first predefined period has elapsed;

determining a dew point temperature for the interior space based on the measured temperature and relative humidity;

determining if the determined dew point temperature is above a predetermined dew point temperature; and

if the determined dew point temperature is above the predetermined dew point temperature

turning on the compressor of the dehumidifier,

drawing air to be dehumidified from at least the HVAC return duct through at least at least one dehumidifier return duct;

dehumidifying the drawn air; and

returning the dehumidified air to at least the HVAC supply duct through at least at least one dehumidifier supply duct.

29. The method of claim 28, wherein waiting for the first predefined period comprises waiting for two minutes.

30. The method of claim 28, wherein:

determining if a measurement event has occurred comprises determining if a blower call signal has been output.

31. The method of claim 30, wherein:

the dehumidifier has a current air cycle interval; and

determining if a blower call signal has been output comprises determining if the output blower call signal is a first blower call signal of the current air cycle interval.

32. The method of claim 31, wherein determining if a measurement event has occurred further comprises determining that a measurement event has occurred only if the output blower call signal is the first blower call signal of the current air cycle interval.

33. The method of claim 28, wherein:

the dehumidifier has a current air cycle interval; and

determining if a measurement event has occurred comprises determining that a measurement event has occurred only if the current air cycle interval is within the first predefined interval before the end of the current air cycle interval and no blower call signals have been received during the current air cycle interval.

34. The method of claim 33, wherein determining that a measurement event has occurred only if the current air cycle interval is within the first predefined interval before the end of the current air cycle interval comprises determining that a measurement event has occurred only if the current air cycle interval is within three minutes before the end of the current air cycle interval.

35. The method of claim 28, wherein:

the dehumidifier is located outside of the at least one interior space to be dehumidified such that the temperature and relative humidity sensors are outside of the at least one interior space; and

measuring the temperature and the relative humidity of an ambient atmosphere within the housing using the temperature and relative humidity sensors comprises measuring the temperature and relative humidity of air outside of the at least one interior space to be dehumidified.

36. A dehumidifier system usable to automatically dehumidify at least one interior space of a structure, the structure having an HVAC system that includes at least an HVAC blower and that is connected to the interior space through at least one of at least an HVAC supply duct and at least an HVAC return duct, the HVAC blower turned on by the HVAC system in response to blower call signals, the dehumidifier system associated with the HVAC system and comprising:

a compressor;

a dehumidifier blower;

a temperature sensor;

a relative humidity sensor;

a housing, the compressor, the blower, the temperature sensor and the relative humidity sensor contained within the housing;

a control system;

at least one dehumidifier return duct; and

at least one dehumidifier supply duct, wherein;

the housing is at least indirectly connected to the at least one interior space by the at least one dehumidifier return duct and the at least one dehumidifier supply duct,

the control system determines whether a measurement event has occurred;

the control system, in response to an occurrence of a measurement event, determines if the HVAC system is in a blower mode;

the control system, in response to the HVAC system being in a blower mode, determines if the HVAC blower is on and, if the blower is not on, turns on the blower;

the control system, in response to an occurrence of a measurement event, determines a dew point temperature based on a temperature and a relative humidity of an ambient atmosphere within the housing as measured by the temperature and relative humidity sensors, and determines, if the determined dew point temperature is above a predetermined dew point temperature, and

the control system, in response to the determined dew point temperature being above the predetermined dew point temperature, turns on the compressor of the dehumidifier and if the dehumidifier blower is not on, turns on the dehumidifier blower, such that air to be dehumidified is drawn from at least the at least one interior space through at least the at least one dehumidifier return duct, dehumidified and returned to at least the at least one interior space through at the least the at least one dehumidifier supply duct.

37. The dehumidifier system of claim 36, further comprising a set of coils comprising at least one coil, wherein:

the at least dehumidifier return duct supplies a stream of air to be dehumidified to the housing that is at least indirectly drawn from the interior space;

at least one of the temperature and humidity sensors are located within the housing such that the at least one of the temperature and humidity sensors is upstream of the at least one coil and the at least one of the temperature and humidity sensors senses the at least respective one of the temperature and humidity of the air supplied to the housing to be dehumidified.

38. The dehumidifier system of claim 37, wherein the at least one of the temperature and humidity sensors that is located within the housing projects into the stream of air supplied from the at least one dehumidifier return duct.

39. The dehumidifier system of claim 38, wherein the at least one of the temperature and humidity sensors that is located within the housing projects into a central portion of the stream of air supplied from the at least one dehumidifier return duct.

40. The dehumidifier system of claim 36, wherein, in response to the occurrence of a measurement event, the control system operates the blower of the dehumidifier for at least a first time period before inputting the at least one of the temperature and humidity measurements from the at least one of the temperature and humidity sensors that is located within the housing.

41. The dehumidifier system of claim 36, further comprising a dew point setting device connected to the control system, the dew point setting device inputting the set dew point temperature to the control system.

42. The dehumidifier system of claim 41, wherein, when the dew point setting device is operated to change the set dew point temperature by a least a first amount, the control system determines that a measurement event has occurred.

43. The dehumidifier system claim 36, wherein the temperature and relative humidity sensors are located outside of the at least one interior space.

44. The dehumidifier system of claim 36, wherein the control system determines if the HVAC system is currently responding to a cooling call or has finished responding to a cooling call within a first time period of receiving the measurement event, and, if the HVAC is currently responding to a cooling call or has finished responding to a cooling call within a first time period of receiving the measurement event, the control system waits until the first time period has elapsed since the HVAC system has finished responding to the cooling call before proceeding to respond to the measurement event.

45. The dehumidifier system of claim 36, wherein:

the HVAC system includes at least one HVAC system control device that outputs blower call signals;

the control system receives blower call signals output by at least one of the at least one HVAC system control device; and

the control system determines that a measurement event has occurred when the control system receives a first blower call signal within an air cycle interval.

46. The dehumidifier system of claim 45, further comprising an air cycle interval setting device connected to the control system, the air cycle interval setting device inputting the air cycle interval to the control system.

47. The dehumidifier system of claim 36, wherein:

the HVAC system includes at least one HVAC system control device that outputs blower call signals;

the control system receives blower call signals output by at least one of the at least one HVAC system control device; and

the control system determines that a measurement event has occurred when the control system has not received a first blower call signal before an occurrence of a first point in time before an end of an air cycle interval.

48. The dehumidifier system of claim 47, further comprising an air cycle interval setting device connected to the control system, the air cycle interval setting device inputting the air cycle interval to the control system.

49. The dehumidifier system of claim 36, wherein:

the HVAC system includes at least one HVAC system control device that outputs blower call signals;

the control system receives blower call signals output by at least one of the at least one HVAC system control device and outputs blower call signals to the HVAC equipment control device; and

in response to the occurrence of a measurement event, the control system determines if the HVAC system is in a blower mode, and, if the HVAC system is in a blower mode, outputs a pseudo blower call to the HVAC equipment control device.

50. The dehumidifier system of claim 36, wherein:

the HVAC system includes at least one HVAC system control device that outputs blower call signals;

at least one of the at least one dehumidifier supply duct is connected to the HVAC supply duct and includes a controllable damper connected to the control system;

at least one of the at least one dehumidifier supply duct is connected to the interior space and includes a controllable damper connected to the control system;

the control system, in response to the occurrence of a measurement event, determines if the HVAC blower is on; and

the control system, if the HVAC blower is on, operates the dampers in the at least one dehumidifier supply ducts to open the at least one dehumidifier supply duct that is connected to the HVAC supply duct and to close the at least one dehumidifier supply duct that is connected to the interior space.

51. The dehumidifier system of claim 50, wherein the control system, if the HVAC blower is not on, operates the dampers in the at least one dehumidifier supply ducts to close the at least one dehumidifier supply duct that is connected to the HVAC supply duct and to open the at least one dehumidifier supply duct that is connected to the interior space.

52. The dehumidifier system of claim 50, wherein:

at least one of the at least one dehumidifier return duct is connected to the HVAC return duct and includes a controllable damper connected to the control system;

at least one of the at least one dehumidifier return duct is connected to the interior space and includes a controllable damper connected to the control system; and

the control system, if the HVAC blower is on, operates the dampers in the at least one dehumidifier return ducts to open the at least one dehumidifier return duct that is connected to the HVAC return duct and to close the at least one dehumidifier return duct that is connected to the interior space.

53. The dehumidifier system of claim 52, wherein the control system, if the HVAC blower is not on, operates the dampers in the at least one dehumidifier return ducts to close the at least one dehumidifier return duct that is connected to the HVAC return duct and to open the at least one dehumidifier supply duct that is connected to the interior space.

54. The dehumidifier system of claim 50, wherein:

at least one of the at least one dehumidifier return duct is connected to the HVAC return duct and includes a controllable damper connected to the control system;

at least one of the at least one dehumidifier return duct is connected to the interior space; and

the control system, if the HVAC blower is on, operates the damper in the at least one dehumidifier return duct to open the at least one dehumidifier return duct that is connected to the HVAC return duct.

55. The dehumidifier system of claim 54, wherein the control system, if the HVAC blower is not on, operates the damper in the at least one dehumidifier return duct to close the at least one dehumidifier return duct that is connected to the HVAC return duct.

56. The dehumidifier system of claim 50, wherein:

at least one of the at least one dehumidifier return duct is connected to the HVAC return duct;

at least one of the at least one dehumidifier return duct is connected to the interior space and includes a controllable damper connected to the control system; and

the control system, if the HVAC blower is on, operates the damper in the at least one dehumidifier return duct to close the at least one dehumidifier return duct that is connected to the interior space.

57. The dehumidifier system of claim 56, wherein the control system, if the HVAC blower is not on, operates the damper in the at least one dehumidifier return ducts to open the at least one dehumidifier supply duct that is connected to the interior space.

58. The dehumidifier system of claim 36, wherein the control system operates the compressor for at least a first time period.

59. The dehumidifier system of claim 58, further comprising:

a set of coils; and

a frost sensor associated with the set of coils, the frost sensor outputting a measured frost temperature to the control system, wherein;

after the control system operates the compressor for at least the first time period, the control system determines if the measured frost temperature is less than a first temperature, and

if the measured frost temperature is less than a first temperature, the control system determines an amount of time that the measured frost temperature has been less than a first temperature.

60. The dehumidifier system of claim 59, wherein, if the determined amount of time is greater than a first amount of time, the control system turns off the compressor, waits for a second time period, inputs the measured frost temperature and determines if the measured frost temperature is at least equal to a second temperature.

61. The dehumidifier system of claim 60, wherein the control system continues to input the measured frost temperature and determine if the measured frost temperature is at least equal to the second temperature until the measured frost temperature is at least equal to the second temperature.

62. The dehumidifier system of claim 59, wherein, if the measured amount of time is not greater than the first amount of time, the control system again determines the measured dew point temperature of the air to be dehumidified and, if the measured dew point temperature is above the set dew point temperature, the control system again operates the compressor for at least the first time period.

63. The dehumidifier system of claim 59, wherein, if the measured amount of time is not greater than the first amount of time, the control system determines the measured dew point temperature of the air to be dehumidified, and, if the measured dew point temperature is not above the set dew point temperature, the control system turns off the dehumidifier compressor and blower.

64. The dehumidifier system of claim 59, wherein, if the measured frost temperature is not less than the first temperature, the control system again determines the measured dew point temperature of the air to be dehumidified, and, if the measured dew point temperature is above the set dew point temperature, the control system again operates the compressor for at least the first time period.

65. The dehumidifier system of claim 59, wherein, if the measured frost temperature is not less than the first temperature, the control system again determines the measured dew point temperature of the air to be dehumidified, and, if the measured dew point temperature is not above the set dew point temperature, the control system turns off the dehumidifier compressor and blower.

66. The dehumidifier system of claim 36, wherein, if the dew point temperature of the air to be dehumidified is not above the set dew point temperature, the control system turns off the dehumidifier blower if it is running and the HVAC blower if it is running.

67. The dehumidifier system of claim 36, wherein:

the HVAC system includes, an HVAC equipment control device that controllably operates at least the HVAC blower in response to blower call signals, at least one HVAC system control device that outputs blower call signals and at least one ventilation duct connected to the HVAC return duct and that includes a controllable damper connected to the control system;

the control system, in response to the occurrence of a measurement event, determines if the HVAC blower is on; and

the control system, if the HVAC blower is on, operates the damper in the at least one ventilation duct to open the at least one ventilation duct to supply outside air to the HVAC system.