CA2520975A1

CA2520975A1 - Apparatus and control method for ventilation and air conditioning economizer

Info

Publication number: CA2520975A1
Application number: CA002520975A
Authority: CA
Inventors: Weihai Xue
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-10-04
Filing date: 2005-10-04
Publication date: 2007-04-04

Abstract

A control system and method for space ventilation and air conditioning economizer operation are disclosed. An economizer hood ventilator and its control cente r, integrating the operation of other space heating ventilation and air conditioning apparatus, are further disclosed. This low cost economizer hood ventilator and its control center a re invented mainly for both existing and future residential houses to meet controlled fresh air ventilation requirements. The manual operated principal ventilation switch can override any other automatic ventilation controls. When ambient air is available for free cooling, the system works as air conditioning economizer.

Description

Description Apparatus and control method for ventilation and air conditioning economizer Field of this invention This invention relates generally to residential mechanical ventilation systems in which the economizer hood ventilator and its control center are utilized to integrate the operation of other heating, ventilation and air conditioning devices for meeting the ventilation requirement in the 1995 national building code and CAN/CSA-F326 residential mechanical ventilation systems, and for free cooling the residential buildings in cooling seasons.
Background of this invention Modern homes are built more airtight than ever for energy conservation. All dwellings require fresh air to deal with moisture, odors and indoor air pollutants. The requires that new dwellings have mechanical ventilation systems capable of providing this fresh air. Generally, there are two approaches for mechanical ventilation of a house. One of the approaches is to have a fresh air intake hood coupled to forced-air heating furnace return air duct. The other approach is to install a heat recovery ventilator.
Heat recovery ventilators help homeowners save tremendous energy and significantly improve the indoor air quality for airtight houses in wintertime. However, the Heat recovery ventilator does not sense ambient air humidity, and would draw high enthalpy ambient air into the house in hot and humid summertime. Further more, when lower enthalpy ambient air is available for free cooling, the heat recovery ventilator would not supply enough flow rate for free cooling, and the heat recovery cores in the ventilators work in unpleasant way to warm up incoming cooling air. Homeowners can only rely on opening and closing the windows and doors for ventilation and free cooling purposes, but would normally fail to follow the ambient air temperature and humidity level changes closely enough.
On the other hand, many homeowners would not open windows at night, due to noise, security, and insert concerns.

-2-The greatest shortfall of a system of available technology that complies with CAN/CSA-F326, relative to the ideal system, is in the area of control. First of all, the mechanical ventilation system should be demand-controlled systems, and the system's on/off manual switch should be able to override any automatic controls, such as de-humidistat, carbon deoxidizes sensor. Furthermore, mechanical ventilation devices should not interference with other systems: they should not depressurize the houses for more than 5 Pa and should not pressurize the house for more than 10 Pa. And there are still some other requirements, such as distribution of fresh air; the fresh air intake should not cause the return air temperature fall below 15.5 ° C before the mixed air reaches the furnace heat exchanger. The system should not over ventilate the house; and the systems should be able to maximize the outdoor air usage when it is available for free cooling.
In the other word, the ventilation system should be energy-efficient, easy to control, lower in cost to install and maintain, and demand-controlled ventilation system.
In cold dry climates, there is normally a significant temperature and humidity level difference between nighttime and daytime. There always have been some cooling demands for these houses in summertime, regardless there is a central air conditioning system installed or not. Houses are usually occupied at night when the ambient air is available out there for free cooling. So we can always relay on existing blower in the forced-air heating furnace, and the high capacity economizer exhaust fan to draw the lower temperature and lower relative humidity ambient air into the house to maximize the benefit from Mother Nature without having to run the compressor for cooling.
Economizer has been invented for over 20 years, and there are so many types of improvement have been made available for roof top units on top of those commercial, institutional and even industrial buildings. And there are still only limited kinds of economizer designed for residential use. But none of them can be used to integrate the operation of other heating, ventilation and air conditioning devices. Because of the initial installation cost, maintenance cost, reliability concerns and incompatible with existing heating ventilation and air conditioning devices, so the economizer of prior arts fails to satisfy the average homeowners' requirements.

-3-Description of prior art It is known in the prior art to integrate the economizer operation with the operation of an air conditioning system to effect cooling of an enclosure. Canadian patent number CA
1165566, which was issued to Gilson on Apr. 17, 1984, for example, discloses an economizer control method to utilize staged cooling load and outdoor air temperature to select the appropriate mode of operation by modulating economizer damper position through motor locking circuits and spring return means. For instance, Canadian patent number CA 1157649 to Hile, which was issued on Nov. 29, 1983, shows a rooftop type air conditioning unit have a economizer for drawing low enthalpy ambient air into the enclosure with a multiple speed fan. For example, Canadian patent number CA
1221436 to Smith, issued on May 5, 1987, disclosed an economizer with many temperature and enthalpy sensors to offer substantial flexibility in the operation.
Similarly, Canadian patent number CA 2108327, which was issued on Oct. 10, 1995, disclosed two sections economizer damper for providing improved air mixing.
United States Patent 6804975, Issued on October 19, 2004, disclosed an air conditioning unit with a ventilation damper which can be freely adjusted in a range of 0 to 100% without additional equipment, and it will recover the energy from stale air with heat exchanger.
United States Patent 6826920, Issued on December 7, 2004, concerns high humidity level in a commercial building with rooftop unit controlled by indoor dry bulb thermostat, disclosed a dehumidification system integrated with damper controlled air handling unit by slowing down the movement of air across the cooling coil to dehumidify the air in the enclosure.
Economizer control methods of prior art mainly concerns roof top unit, they help business owners save large sums of electricity consumption each year. But economizer control methods of prior arts fail to teach an economizer control method that can be utilized to

-4-integrate the operations of existing forced-air heating and air conditioning systems with the most popular low voltage room thermostat control.
On the other hand, the study has led to a conclusion that temperature based economizer cycle save more energy than enthalpy based economizer cycle in a climate from dry to moderate humidity level. In hot, humid climate, an economizer should not be used regardless which economizer control method is utilized.
Furthermore, the relative humidity level in residential homes are all different, some houses may already have high humidity concerns, some houses may have less high humidity level concerns.
So, the homeowners are in needs for a type of economizer in which the data collection of ambient air temperature and humidity level is simply and reliable, and the dry bulb temperature and relative humidity set point could be adjusted easily and separately.
Canadian patent CA 2326241, Issued on April 13, 2004, introduces a fresh air intake weather hood with a removable pre-filtering devices to admit fresh air into a house. But there was no home ventilation control method has been told to satisfy both ventilation and economizer operation requirements.
It is apparent from foregoing that the prior art fails to teach an economizer control method in which economizer damper could be directly controlled by adjustable ambient thermostat and ambient humidistat. The prior art further fails to teach, or even suggest, an ventilation and economizer control method that can be utilized to integrate the existing popular low voltage thermostat controlled forced-air heating, and air condition system devices for both fresh air ventilation and economizer operation. And thus prior art fail to satisfy residential homeowners with a low cost economizer and ventilation control method and apparatus that complies with mechanical ventilation requirements in the and CAN/CSA F-326 residential mechanical ventilation system.

-5-Summary of the invention According to one aspect of the invention, there is provided an economizer hood ventilator control system in which the damper operation is controlled by whole house principal ventilation switch, room thermostat fan switch, de-humidistat, demand-controlled ventilation sensor, mechanical timer switch, cooling demand from indoor room thermostat, ambient air thermostat and ambient air humidistat. Together with the fan control centers, the economizer hood ventilator is used to control the fresh air intake damper, the whole house principal ventilation exhaust fan, the high capacity economizer exhaust fan and the economizer in-line booster fan.
This invention utilizes heating only mechanical thermostat and mechanical humidistat for sensing ambient dry bulb temperature and relative humidity level. The economizer damper operation is controlled directly by mechanical switches and relays. So, it is simple in installation and maintenance, and it is reliable in operation. The most important point is that the economizer hood ventilator and its control center is affordable for average homeowners, and it is energy-efficient solutions for house cooling and ventilation purpose.
This invention possesses numerous benefits and advantages over known economizers for residential homes. The economizer hood ventilator and its control center are compatible with any type of low voltage thermostat. And it is compatible with any type of forced-air heating furnaces.
In addition to the foregoing attributes, the economizer hood ventilator, together with its control center and manual ventilation switch can also be used to control the whole house ventilation to meet the1995 NBC and CAN/CSA F326 ventilation requirements.

-6-Brief description of the drawings Fig. 1 is a side cross-sectional schematic view of an economizer hood ventilator as it appears when the damper is at open position and the door of economizer hood ventilator is closed.
Fig. 2 is a side cross-sectional schematic view of the economizer hood ventilator as it appears when the motor is powered to close the damper, and the door is left open.
Fig. 3 is schematic front plan view and side view of an economizer hood ventilator, as it appears when the front door assembly is removed.
Fig. 4 is a partial wiring schematic of a control circuit for an economizer hood ventilator to be used with an economizer hood ventilator control center and other home heating, ventilation and air conditioning devices.
Fig. 5 is a schematic section view of a typical application of an economizer hood ventilator and its control center installed in a house with a forced-air heating furnace. The drawing shows the location for each component in the system and wire or cable connections between each component that directly related to this invention.
Description of the preferred embodiment In the forgoing description, the economizer hood ventilator is abbreviated as EHV, and the economizer hood ventilator control center is shortened to be EHV control center.
The construction of an economizer hood ventilator

-7-As depicted in Fig. 1 and Fig 3, the EHV body assembly 2 is defined by an EHV
body 24, a through wall ventilation pipe 5, a mitered reducer fitting 6, a round to square transfer plate 28, a motor installation channel 7, a damper shaft 32 mounting channel 18, a top door frame 9, a bottom door frame 23, a foam sealing tape 19, two bird screen tracks 22, one fixed side of lockable door catch 26. Except for foam sealing tape 19, the rest parts of EHV body assembly 2 are made of galvanized sheet metal, and they are spot welded together. The foam sealing tape 19 is to make sure the EHV is of rain-water-proofed construction. Based on the normal ventilation requirements for modern homes, the diameter of through wall ventilation pipe 5 is 6-inch. The diameter of ventilation pipe 5 can be changed for different ventilation flow rate requirement. The mitered reducer fitting 6 is to minimize the resistance for the airflow stream 41.
As depicted in Fig. 1 and Fig. 2, EHV door assembly 21 is defined by a door panel 25, a thermo insulation foam 12, an accessory mounting plate 14, a thermostat mounting box 10, a swinging side of lockable door catch 27, and two of door hitches 11. The accessory mounting plate 14 and door panel 25 are of galvanized sheet metals. The accessory mounting plate 14 is spot-welded to the door panel 25 after the thermo insulation foam 12 is placed inside. The swinging side of zinc plated lockable door catch 27 is spot welded to door panel 25. The thermostat mounting box 10 is galvanized standard 4-inch by 2-inch electrical metal box, fastened to the accessory mounting plate 14 with sheet metal screws.
Two of zinc plated door hitches 11 are spot welded to the door panel 25.
Thermo insulation foam 12 is placed between accessory mounting plate 14 and door panel 25 to minimize the sunlight radiation heat affect to the ambient thermostat 13.
As depicted in Fig. 3, the damper assembly 3 is defined by a damper plate 33, a shaft 32, a nylon bearing 29, a coupling 30, two of setscrews 31 and damper sealing foam 4. The damper plate 33 is of galvanized sheet metal. The shaft 32 is of 0.25 inch in diameter galvanized pencil rod. The damper plate 33 is spot welded to the shaft 32. The coupling 30 and two of setscrews 31 are used to connect damper assembly 3 to damper motor 8.
Damper sealing foam 4 is to seal the gap between reducer fitting 6 and damper plate 33.

_$_ With reference to the Fig. 1, Fig. 2 and Fig 3, the EHV 20 comprises a heating only mechanical thermostat 13, a mechanical humidistat 16, a damper motor 8, a damper assembly 3, an EHV body assembly 2, a door assembly 21, a bird screen 1, a 4-poles terminal block 17 and a damper return spring 15. The thermostat 13 is a popular low cost heating only mechanical thermostat that would be normally used for baseboard heater.
The mechanical humidistat 16 is a regular low cost humidistat that would be normally used for home humidifier, it has nylon-sensing element built inside. The damper motor 8 is 5 Watts, 24 VAC, and synchronous motor with gear reduction unit built inside the motor.
The shaft position of damper motor 8 can be spring-returned, when the power supply is removed. The EHV door assembly 21 is fastened to the EHV body assembly 2 with 4 sets of zinc plated countersink head screws and nuts. The damper motor 8 is mounted to the EHV body assembly 2 with two sets of 0.125-inch zinc plated hex screws and nuts. The bird screen 1 is of 0.25-inch by 0.25-inch galvanized bird screen material with protective edge of galvanized sheet metal; the bird screen has a free flow area more than three times of through wall pipe 5 as per 1995 NBC. The bird screen can be slid into the tracks 22 that attached to the EHV body assembly 2, and it can be removed for cleaning without using any tools. The mechanical thermostat 13 is mounted on an electrical box 10 that attached to the door assembly 2, it has a knob 29 that can be turned and set at desired ambient air temperature range, normally set at 24 °C. The mechanical humidistat 16 is mounted on the accessory mounting plate 14, it has a knob 30 that can be turned and set at predetermined ambient air relative humidity level, normally set at 60%. As illustrated in Fig. 3 and Fig. 5, The EHV body assembly 2 has four small holes 34 that can be used to mount EHV 20 to the outside wall of a house. Referring to Fig. 3, the EHV
20 has a big hole 35 to run four of 18 gauge control wires through the wall of a house for connection between the terminal block 17 and the EHV control center 36 as illustrated in Fig. 4.
Mechanical functions of an EHV 20 As depicted in Fig.2, when the damper motor 8 is powered to close the damper, the ambient air stream rises from stream 39 to stream 40. As the ambient air stream passes _g_ through the mechanical humidistat 16 and mechanical thermostat 13, the mechanical thermostat 13 and humidistat 16 could reflect true ambient temperature and humidity level even with the door of EHV 20 closed,.
As illustrated in Fig.1 and Fig 5, when the damper motor 8 is without power, the damper plate 33 is pulled back by spring 15, so the economizer hood ventilator damper will open to facilitate ventilation or economizer cooling operation. The blower or air circulation fan in the forced-air heating furnace 47 would draw air from stream 37 and 38 to stream 41, and than mixed up with return air stream 120, and sent to supply air stream 123 of the forced-air heating cooling or ventilation system in a house. The damper assembly 3 is designed to open whenever there is a power failure, as per CAN/CSA-F326 residential mechanical ventilation systems requirement.
The wire connections inside an EHV 20 and an EHV control center 36, and between each components in the whole ventilation and economizer system Referring now to Fig. 4, there can be seen an EHV control center 36 connecting an EHV
20, a transformer 42 with 24 VAC output, a manual operated principal ventilation switch 43, a forced-air heating furnace 47, a room thermostat 46, a demand-controlled ventilation sensor 44, a room de-humidistat 45, a mechanical timer switch 128, a economizer exhaust fan control center 52, a in-line booster fan control center 50, a principal ventilation fan control center 48. All the wires connecting the components inside the EHV control center 36, and all the wires between EHV control center 36 and other directly connected components is of low voltage, 18GA copper HVAC control wire.
As illustrated in Fig. 4, the EHV 20 has four electrical components: a damper motor 8, a mechanical heating only thermostat 13, a mechanical humidistat 16, and a four pole terminal block. All the wires connecting each components inside an EHV 20 is of 18GA
copper HVAC control wires. The damper motor 8 is connected to terminal block MOD
through wire 71 and wire 72. The damper motor 8 is of synchronous motor with gear reduction unit built inside. The position of damper assembly 3 can be spring-returned, according to Fig. 2, when the power supply is removed. The mechanical heating only thermostat 13 has a snap action switch built inside, whenever the ambient temperature drop below the set point, the contact of thermostat 13 snap action switch will become closed. The humidistat 16 has a nylon ribbon-sensing element built inside together with a normally open snap-action-contact switch. Whenever the ambient relative humidity level is lower than the preset value, the contact will become close. The thermostat THE 13, and humidistat HUM 16 are connected in series, and they are connected to terminal block ECO through wire 73, wire 74, and wire 75. The connections between terminal block MOD in the EHV 20 and MOD in the EHV control center 36 are field wired through wire 92 and wire 93. The terminal block ECO in the EHV 20 and ECO in the EHV
control center 36 are also field wired and connected together through wire 90 and wire 91.
As illustrated in Fig. 4, the transformer 42 is to be installed separately.
The transformer is installed in a location that is close to the EHV control center 36. The input of transformer 42 is 115VAC, connected to power supply with 14 gauge copper wires. The power supply to transformer 42 is accomplished by wire connections inside a standard 2-inch by 4-inch electrical box. The transformer 42 has an output voltage 24VAC with 20VA
capacity. The transformer 42 supplies the power to economizer relay ER, in-line booster fan relay IR
and the damper motor 8.
As illustrated in Fig. 4, the EHV control center 36 comprises a cooling relay CR, a principal ventilation relay PR, an economizer relay ER, an in-line booster fan relay IR, and two of 8 poles terminal blocks. All the relays and terminal blocks of an EHV
control center 36 can be installed inside an off-shelf metal ventilation control box. The cooling relay CR
is of White-Rodgers SPNO-SPNC switching relay with a coil rating of 24VAC 3VA.
The cooling relay CR connected to Y and COM terminals of terminal block through wire 54 and wire 55. The cooling relay CR has one normally close contact CR1, connecting principal ventilation relay PR and COM terminal of terminal block through wire 56 and wire 57. The cooling relay CR has one normally open contact CR2, connecting economizer relay ER with in-line booster fan relay IR in parallel, and one of the terminal at terminal block of 24V power supply through wire 60 and wire 61. The principal ventilation relay PR is of White-Rodgers SPNO-SPNC switching relay with a coil rating of 3VA. The principal ventilation relay PR connecting CR1 and terminal PV through wire 57 and 58. The principal ventilation relay PR has one normally close contact PR1 connecting normally close contact ER1 of economizer relay ER and one of the terminals at motor operated damper terminal block MOD through wire 62 and wire 63. The principal ventilation relay PR has one normally open contact PR2 connecting terminal PVF
through wire 69 and 70. The economizer relay ER is of White-Rodgers SPNO-SPNC
switching relay with a coil rating of 24VAC 3VA. The economizer relay ER connecting one of the terminals at terminal block ECO and normally open cooling relay contact CR2 through wire 60 and wire 59. The economizer relay ER has one normally close contact connecting PR1 and one terminal of the power supply terminal block 24V though wire 61 and wire 62. The economizer relay ER has one normally open contact ER2 connecting terminal EEF through wire 65 and wire 66. The in-line booster fan relay IR is of White-Rogers SPST standard relay with a coil rating of 24VAC 3VA. The in-line booster fan relay IR is connected to economizer relay ER in parallel through wire 59 and 60. The in-line booster fan relay IR has a normally open contact IR1 connecting the terminal block IBF through wire 67 and wire 68. The common terminals of terminal blocks of 24V, MOD, ECO is to be connected together through wire 64.
Referring to Fig. 4, the principal ventilation switch PVS 43 has a normally open contact that can be manually operated to override other automatic control in the system. The principal ventilation switch PVS 43 is to be connected to terminals G and PV
of the EHV
control center 36 through wire 78 and wire 79, when field-installed. The principal ventilation switch 43 is a SPST ON/OFF regular switch, normally installed close to room thermostat 46.
Referring to Fig. 4 again, the demand-controlled ventilation sensor 44, room de-humidistat 45 and mechanical timer switch 128 are connected to G and R
terminals of room thermostat 46 in parallel through wire 88 and wire 89. These are optional automatic control. They are normally installed in living space.

As showed in Fig. 4, the forced-air heating furnace 47 is of any type of furnace with 24VAC control terminal blocks, marked as Y, R, COM, G and W. The G and COM
terminals in the EHV control center 36 are to be field-connected to G and COM
terminals in the forced-air heating furnace 47 through wire 80 and wire 81. The Y
terminal of EHV
control center 36 is to be field-connected to Y1, first stage cooling coil terminal of a two-stages room thermostat 46 through wire 82. If the thermostat 46 is a single stage room thermostat, the Y terminal in the EHV control center 36 should be directly connected to Y
terminal in the forced-air heating furnace 47 and the Y terminal in a room thermostat 46 as well. The RC and RH terminals in a room thermostat 46 should be field-connected with wire 85 or the jumper supplied by a thermostat manufacture.
As showed in Fig. 4, there are three fan control centers: the fan control center EFC 52 for an economizer exhaust fan EF 53; the fan control center IFC 50 for an in-line booster fan 51; and the fan control center PFC 48 for a principal exhaust fan 49. The fan control centers could be White-Rogers type 8A05A-101 fan control centers, they all have a transformer and a relay combination for easy installation on a standard 4-inch by 4- inch junction box. The fan control centers are to be installed close to their fans per electrical code. The R and G terminals in the economizer exhaust fan control center EFC
52 are to be connected to the EEF terminals in EHV control center 36 through wire 98 and wire 99.
The R and G terminals in the in-line booster fan control center IFC 50 are to be connected to the IBF terminals in EHV control center 36 through wire 96 and wire 97. The R and G
terminals in the principal ventilation fan control center PFC 48 are to be connected to the PVF terminals in EHV control center 36 through wire 95 and wire 94. The wires for all the fans and their control centers connecting to 115 VAC power supplies, including line voltage wire, neutral wire and ground wire, should be of 14ga copper wires or per manufacture's instructions, and per local electrical code.
As depicted in Fig. 4, cooling relay CR and principal ventilation relay PR in the EHV
control center 36 are of White-Rodgers SPNO-SPNC switching relay with 3VA coil rating.
Whenever cooling relay is energized, the contact of CR1 will be open, in order to prevent the principal ventilation relay PR from being energized. So the maximum extra power consumption from the forced-air heating furnace 47 is only 3VA. The forced-air heating furnace 47 would normally have a transformer with 40VA capacity build inside.
As depicted in Fig. 1 and Fig. 4, the damper motor 8 can be disconnected from power to allow spring 15 to pull the damper assembly 3 open only when the blower in a forced-air heating furnace 47 is running, as long as the transformer 42 has power supply.
Because the blower in a forced-air heating furnace 47 runs whenever the G terminal in room thermostat 46 is energized in both ventilation and economizer operation mode, so the ambient fresh air distribution requirement in the 1995 National Building Code can always be satisfied.
The installation of an EHV 20, an EHV control center 36 and other components in a residential house As illustrated in Fig. 5, an EHV control center 36 could normally be installed in the furnace room 121. All the control wires connecting EHV control center 36 is of 18 Gauge copper wire. Four wires cable 107, actually wire 90, wire 91, wire 92, wire 93 in Fig. 4, connects EHV 20 and EHV control center 36. Two wires cable 124, actually wire 76 and wire 77 in Fig. 4, connects transformer 42 and terminal 24V at EHV control center 36. Two wires cable 108, actually wire 96 and wire 97 in Fig. 4, connects in-line booster fan control center 50 and EHV control center 36. Two wires cable 101, actually wire 78 and wire 79 in Fig. 4, connects principal ventilation switch 43 and EHV control center 36.
Three wires cable 106, actually wire 80, wire 81, wire 82 in Fig. 4, connects the EHV
control center 36 and the forced-air heating furnace 47. Four wires cable 102, actually wire 94, wire 95, wire 98, wire 99 in Fig. 4, connects the EHV control center 36 to the principal ventilation fan control center PFC 48 and the economizer fan control center EFC 52 in the attic 122.
Depends on the convenience for locating each component and lower voltage wiring, the EHV control center could be installed in attic 122 or some other locations instead.

As illustrated in Fig.S, the EHV 20 should be installed outside the wall, at least 18 inch off the ground, and at least 3 feet away from any house exhaust opening as per local ventilation code and building code. The EHV 20 should be away from air contamination source. It is preferred that the EHV 20 is at north side of the home building, so the sunlight has minimum effect on economizer operation in summertime. The duct pipe connecting EHV 20, in-line booster fan 51 and return air duct should be insulated to prevent condensation. There is a manual volume damper 110 installed between and in-line booster fan 51 for air balancing. The home ventilation rate should be calculated per 1995 national building code and CAN/CSA-F326. Based on home ventilation requirement and maximum flow rate allowed for keeping the temperature of return air stream 120 above 15.5 ° C. When balancing and measuring the ventilation flow rate, the blower in the forced-air heating furnace 47 should be set to run at maximum speed, and measure the flow rate after the power supply to transformer 42 has been removed for at least 30 seconds. The flow rate could be measured and adjusted through adjusting manual damper 110. In the case of home ventilation requirement flow rate exceeds the maximum flow rate allowed to satisfy the temperature limit, such as in extreme cold region, an in-line duct heater with its own temperature sensor and control should be installed to make sure that the temperature of return air stream120 is always above 15.5 °C.
As illustrated in Fig.S, the in-line booster fan 51 could be installed between return air duct 117 and manual damper 110, when the house has negative static pressure concerns.
Three wire cable 111: line, natural and ground, connects in-line booster fan 51 and its fan control center IFC 50. An in-line booster fan 51 and fan control center are needed, only when the economizer fan 53 is running and the house could be depressurized for more than 5 Pa in summertime. In case of in-line booster fan 51 is present, the ventilation flow rate should be measured and balanced after the in-line booster fan 51 is installed.
As illustrated in Fig.S, the economizer exhaust fan 53, the principal ventilation fan 49 and their fan control center 48 and 52 could normally be installed in attic 122.
Principal ventilation fan 49 can handle 50 % of home minimum ventilation requirement, and the other 50 % of ventilation requirement can be satisfied by some other exhaust equipment, such as bathroom exhaust fan 116 with its control 117 and kitchen exhaust fan 118 with its control 119. The capacity of economizer exhaust fan 53 is normally several times the capacity of principal ventilation fan 49, depends on cooling load requirement and noise concerns of occupants. The economizer exhaust fan 53 should be installed in attic 122, away from living space 127, connected to acoustic-lined ceiling exhaust plenum 126 with flexible pipe 125 to minimize the noise affects.
As illustrated in Fig.S, the demand-controlled ventilation sensor 44, room de-humidistat 45, mechanical timer switch 128, principal ventilation switch 43 could be installed close to room thermostat 46 in living space 127.
As illustrated in Fig.S, the bathroom exhaust fan 116 and kitchen exhaust fan 118 are not directly linked to the system of this invention, but they may affect the house static pressure. They are showed in Fig. 5 for reference only.
Functions and applications of EHV 20 and its control method The functions and applications of economizer hood ventilator control system can be explained in following four operating modes:
"Automatic Ventilation Mode": Set principal ventilation switch PVS 43 on, and set fan switch of room thermostat 46 at auto.
As illustrated in Fig. 4, if the principal ventilation switch 43 is turned on, whenever the fan in a forced-air heating furnace 47 is running, the principal ventilation relay PR will be energized to allow ambient air to be drawn into the return air duct of a forced-air heating furnace 47, unless the room thermostat 46 calls for cooling. When fan switch in room thermostat 47 set at auto, the blower in the forced-air heating furnace 47 can be activated by heating and cooling demand from room thermostat 46, room de-humidistat 45, demand-controlled ventilation sensor 44 and mechanical timer switch 128. The room de-humidistat 45 should be turned off for summer cooling seasons operation.
"Economizer mode": The system changes to economizer mode automatically.
As illustrated in Fig. 4 and Fig.3, when the room thermostat 46 calls for cooling, the cooling relay CR will be energized, the contact CR1 will open, and the principal ventilation relay will not be energized. So the ambient air will not be drawn into home, if it is not available for free cooling. In the meantime, if the ambient air temperature is lower than the preset value of mechanical thermostat 13 in the EHV 20 and the ambient air relative humidity level is lower than the preset value of humidistat 16 in the EHV 20, the economizer relay ER and in-line booster fan relay IR can be energized, and the contact of ER1 will open, the damper motor 8 will be disconnected from power to allow spring 15 to pull open the damper assembly 3, the system will be working at economizer operation mode. At economizer operation mode, principal ventilation fan is not running.
"Ventilation On mode": Turn principal ventilation switch PVS 43 on, turn fan switch in room thermostat 46 on.
As illustrated in Fig. 4, if the principal ventilation switch is turned on and the fan switch in room thermostat is set at "on" position, the damper in EHV 20 will always be open, and the blower in heating and cooling apparatus will always be running to bring in fresh ambient air from outdoor, unless the room thermostat 46 calls for cooling. To make sure the system is at "Ventilation On Mode" all the time, the temperature setting in the room thermostat 46 should be set higher than usual, so the room thermostat 46 will not call for cooling unnecessarily.
"Ventilation Off mode": Turn principal ventilation switch 43 off.
As illustrated in Fig. 4, if the principal ventilation switch PVS 43 is turned off, the damper 3 in an EHV 2 will not open unless the system is functioning at "Economizer Mode". The Ventilation Off Mode" can be used in following circumstances: whenever there is smog advisory in summer, or ambient air is extremely cold in winter etc.

Normally, the economizer hood ventilator and its control system can be set at "Automatic Ventilation Mode" for most of the time around the year. Based on the "
Automatic Ventilation Mode " settings, the system will automatically shift between "Economizer Mode" and "Automatic Ventilation Mode" without any external interference.
As illustrated in Fig. 4 and Fig. 5, the flexibility of an economizer hood ventilator system can be achieved by omitting or changing following optional components in the system:
The economizer fan 53, the in-line booster fan 51, and their fan control centers 52 and 50 can all be omitted for existing homes. In this case, the economizer hood ventilator and its control center would still have ventilation function and reduced capacity of economizer function, and the system can still be upgraded to full capacity of economizer system when the house is under major renovation;
The economizer fan 53 can be any type mechanical exhaust fan that installed in attic of an exiting house;
The room thermostat 46 can also be a single stage heating and cooling thermostat with a fan switch. In this case, all the Y terminals in room thermostat 46, the forced-air heating furnace 47 and economizer hood ventilator control center 36 can be connected together through wire 82;
The principal ventilation fan 49 can be any existing principal exhaust fan installed in a house;
The in-line booster fan 51 and the inline booster fan control center 50 are not needed, if there is no negative pressure concerns, negative static pressure is over 5 Pa in an enclosure, when the economizer fan 53 is running. The negative static pressure limit can also be achieved by installing a barometric damper for a house.
A manual ON/OFF switch installed next to the economizer fan 53 and a manual ON/OFF switch next to the optional in-line booster fan 51 would satisfy local electrical code requirement and service needs;
Two of SPDT two-ways switch can be installed at different location to replace the ventilation switch 43. For example, one of the SPDT switch can be installed next to the economizer hood ventilator control center 36 in the basement 121, and the other one can be installed in living space 127;
The forced-air heating furnace 47 can be any type furnace that compatible with low voltage thermostat. It can be a furnace with a cooling coil or without a cooling coil built on top of it. The forced-air heating furnace 47 can also be a merely blower that circulate air in an enclosure for ventilation purpose in any other heating system. In case of a blower-ventilation only system, the duct heater with its own temperature control can be installed in the air intake duct;
Demand- controlled ventilation sensor 44, de-humidistat 45 and mechanical timer switch 128 are optional.
The principal ventilation fan and economizer exhaust fan can be a single fan with at least two speeds. The high-speed operation can be actuated from economizer fan control center 52, and the low-speed operation can be actuated from principal ventilation fan control center 48.

Claims

THE EMBODIMENTS OF THIS INVENTION IN WHICH AN EXCLUSIVE
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Apparatus and control method for both ventilation and economizer operation of an enclosure including:
An economizer hood ventilator means for sensing ambient air temperature, relative humidity and admitting ambient fresh air into an enclosure;
An economizer hood ventilator control center means for integrating the operation of other components in the forced-air heating, ventilation and air conditioning system;
A transformer means for supplying power to said economizer hood ventilator control center;
A forced- air heating furnace means for heating, air conditioning and air circulation in an enclosure;
A two-stages room thermostat means for activating the operation of said forced-air heating furnace and relays in said economizer hood ventilator control center;
An economizer fan means to exhaust warm room air of an enclosure and draw low temperature and lower humidity air into an enclosure;
An economizer fan control center means for accepting control signal from said economizer hood ventilator control center to activate the operation of said economizer fan;
An in-line booster fan means to maximize the flow rate of ambient air intake when the ambient air is available for free cooling;
An in-line booster fan control center means for accepting control signal from said economizer hood ventilator control center to activate the operation of said in-line booster fan;
A principal exhaust fan means for general ventilation in an enclosure;

A principal exhaust fan control center means for accepting the control signal from said economizer hood ventilator control center to activate the operation of said principal exhaust fan;
A demand-controlled ventilation sensor means for automatically activating the blower in said forced-air heating furnace when poor indoor air quality is detected;
A de-humidistat means for automatically activating the blower in said forced-air heating furnace when high humidity level is detected at an enclosure for winter heating season operation;
A mechanical timer means for timely actuating the blower of said forced-air heating furnace;
And a principal ventilation switch means for manually overriding other automatic controls.

2. Apparatus and control method as set forth in claim 1 wherein the economizer hood ventilator means comprising:
A thermostat means for sensing ambient air dry bulb temperature;
A humidistat means for sensing ambient air relative humidity;
A damper assembly means for admitting the ambient air into an enclosure or stopping the ambient air from entering an enclosure;
A damper motor means for operating said damper assembly;
A spring means for keeping said damper assembly at open position when there is no power supply to said damper motor;
A bird screen means for stopping insects and debris from entering an enclosure;
A body assembly means for weatherizing the economizer hood ventilator;
A terminal block means for wire connections between said economizer hood ventilator and said economizer hood ventilator control center;
A door assembly means for attaching and accessing said ambient air thermostat, said humidistat and said terminal block.

3. Apparatus and control method as set forth in claim 1 wherein the economizer hood ventilator control center means comprising: a principal ventilation relay; a cooling relay, an economizer relay; an in-line booster fan relay; two terminal blocks;
and an enclosure.
Said principal ventilation relay has two isolated contacts: single pole normally open and single pole normally close. Said principal ventilation relay can be energized, if the following three conditions are satisfied: first, the G
terminal in said room thermostat according to claim 1 is energized to run blower in said forced-air furnace according to claim 1; second, said principal ventilation switch according to claim 1 is set at on position; third, said cooling relay is not energized. When the said principal ventilation relay is energized, its single pole normally close contact will open to disconnect power supply to said damper motor according to claim 1, and its single pole normally open contact will close to activate said principal fan control center of claim1 to run said principal exhaust fan of claim 1.
Said cooling relay has two isolated contacts: single pole normally open and single pole normally close. Said cooling relay can be energized, if said room thermostat according to claim 1 calls for first stage cooling. When said cooling relay is energized, its single pole normally close contact will open to prevent said principal ventilation relay from being energized, and its single pole normally open contact which is connected to said economizer relay and said in-line booster fan relay will be closed.
Said economizer relay has two isolated contacts: single pole normally open and single pole normally close. Said economizer relay can be energized, if the following two conditions are satisfied: first, the ambient air temperature is lower than the preset value of said ambient air thermostat according to claim 2, and second, the ambient relative humidity are lower than the preset value of said ambient air humidistat according to claim 2. When said economizer relay is energized, its single pole normally close contact will open to disconnect the power supply to said damper motor according to claim 2, so said damper assembly in claim 2 will be pulled open by said spring means according to claim 2 to admit ambient air into an enclosure; its single pole normally open contact will close to activate said economizer fan control center according to claim 1, and to run economizer fan according to claim 1.

Said in-line booster fan relay has one single pole normally open contact. Said in-line booster fan relay can be energized if said economizer relay is energized.
When said in-line booster fan relay is energized, its normally open contact will close to activate said in-line booster fan control center according to claim 1 to run in-line booster fan according to claim 1.

Said terminal blocks have wire connection terminal means for connecting the control wires and 24VAC power wires between said apparatus in claim 1.

4. Apparatus as set forth in claim 1 wherein the economizer hood ventilator comprises a body assembly and a door assembly that are made of galvanized sheet metal for extended outdoor service life.

5. Apparatus as set forth in claim 1 wherein the economizer hood ventilator comprises a mechanical thermostat with a mechanical contact switch built inside, and the setting point of said thermostat can be adjusted by turning the knob on said thermostat.

6. Apparatus as set forth in claim 1 wherein the economizer hood ventilator comprises a mechanical humidistat with a mechanical contact switch built inside, and the setting point of said humidistat can be adjusted by turning the knob on said humidistat.

7. Apparatus as set forth in claim 1 wherein the economizer hood ventilator comprises a damper motor that is a spring-returned synchronous motor.

8. Apparatus of claim 4 wherein said body assembly comprises an opening at top portion for air circulation inside the said economizer hood ventilator, in order for said ambient thermostat and humidistat in claim 2 to reflect the true ambient temperature and true ambient relative humidity level.

9. Apparatus of claim 4 wherein said door assembly comprises a piece of isolation foam to minimize the heat effect from direct sunlight to said mechanical thermostat in claim 2.

10. Apparatus of claim 4 wherein said body assembly comprises a through wall ventilation pipe that is to be connected to return air duct of a forced-air heating furnace according to claim 1.

11. Apparatus of claim 10 wherein said through wall ventilation pipe is attached to a mitered reducer fitting that faces said bird screen in claim 2 to minimize the resistance to airflow.

12. Apparatus of claim 2 wherein said bird screen has a effective free airflow area more than three time of sectional area of said through wall ventilation pipe of claim 10.

13. Apparatus of claim 2 wherein said bird screen is made of galvanized 0.25-inch by 0.25-inch welded screen metal with protective edge of galvanized sheet metal.

14. Apparatus of claim 2 wherein said body assembly comprises two tracks that are tapered and facing away from wall to increase the effective ventilation area and further reduce its resistance to airflow.

15. Apparatus of claim 2 wherein the bird screen is slid into said tracks of claim 14. So said bird screen can be removed for cleaning without using any tools.

16. Apparatus of claim 2 wherein said body assembly comprises a tapered top portion to prevent dirt from accumulating on top of said body assembly.

17. Apparatus of claim 2 wherein said body assembly and door assembly have a lockable catch means to keep a tight seal between said body assembly and door assembly.

18. Apparatus and control method of claim 2 wherein said economizer hood ventilator comprises a mechanical thermostat and mechanical humidistat that have switch contact means to control a damper means for admitting ambient air into an enclosure and operating economizer fan according to claim 1.

19. Apparatus and control method of claim 3 wherein said principal ventilation relay coil can be disconnected from power whenever said cooling relay coil is energized.
So the extra power consumption from the transformer in said forced-air heating furnace according to claim 1 is no more than the power consumption of a single relay.

20. Apparatus and control method of claim 3 wherein said principal ventilation relay coil can be disconnected from power whenever said cooling relay coil is energized.
So the ambient air will not be drawn into the enclosure if the ambient air is not available for free cooling.

21. A control system and method as set forth in claim 1 wherein the method of ventilation operation includes the steps of:
Sensing indoor air quality through said demand-controlled ventilation sensor and de-humidistat, or sensing said mechanical timer setting according to claim 1;
Actuating the blower in force-air furnace through G terminal of said room thermostat or through G terminal of said forced-air furnace according to claim 1, G terminal can also be energized by room thermostat of claim 1;
Energizing ventilation relay of claim 3 if said room thermostat of claim 1 is not calling for cooling and said manual ventilation switch is at on position;
Disconnecting power supply to said damper motor in order for said damper return spring means to open said damper assembly according to claim 2, and actuating said ventilation fan control center to run ventilation fan in claim

22. A control system and method as set forth in claim 1 wherein the method of economizer operation includes the steps of:
Sensing the first stage cooling demand from said room thermostat according to claim 1;
Energizing said cooling relay and preventing said principal relay from being energized according to claim 3, if said room thermostat calls for cooling;
Sensing both ambient air dry bulb temperature and ambient air relative humidity according to claim 2;
Energizing said economizer relay according to claim 3, if room thermostat calls for cooling and ambient air is available for cooling;
Disconnecting power supply to said damper motor in order for said spring to open the damper assembly according to claim 2, and actuating economizer fan control center to run economizer fan in claim 1, and actuating in-line booster fan control center to run in-line booster fan in claim 1, in order to cool the enclosure until the room temperature is satisfied or ambient air is not available for free cooling.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.