Abstract: An air duct type multizone air conditioning system having air dampers and corresponding thermostats in respective zones under the control of a main controller. The main controller can override desired temperatures selected by the corresponding thermostats in any of the zones and automatically detects the number of the number of zones, the presence of an auxiliary heater, and a heat pump, and the presence of an air damper and corresponding thermostat properly located in the same zone. The main controller also receives information regarding the operating cost of the heat pump and the auxiliary heater to ensure their cost-effective use.

Abstract: Heat exchanger apparatus and method for cooling and removing moisture from air passing from a turbocharger (10) and the like to an intake of a combustion engine (11) is illustrated wherein heat pipes (B) extend across a flow path of the compressed air to a zone (C) of ambient air external of the flow path of compressed air to transfer heat to a controlled ambient air flow in the ambient (C) passing across the heat tubes, and including a coalescer zone (D) for collecting and removing moisture from the cooled air.

Abstract: Flue gas is passed through a first heat exchanger, a wet scrubber, and a second heat exchanger. The first heat exchanger supplies heated liquid to the second heat exchanger to reheat the flue gas. The first heat exchanger comprises, and the second heat exchanger ideally comprises, a plurality of fluoroplastic-covered metal tubes extending through a fluoroplastic-lined gas passage.

Abstract: A hot water heating system powered by a gas burner uses the output signal of a heat consumption meter measuring the amount of heat flowing to heating radiators for controlling the heat capacity or heating power of the burner. A control signal dependent on the demand of heat is fed to a solenoid operator of a servopressure regulator and the required amount of air for achieving optimum combustion is supplied via an air control valve which receives its input signal from an oxygen or carbon dioxide sensor in a burner stack.

Abstract: A heat exchange apparatus having a first header for receiving fluid from a source, flexible thin-walled tubular plastic heat exchange elements defining a plurality of passages through a heat exchange zone and second header means for receiving fluid from said plastic heat exchange elements after passing through said heat exchange zone. Support elements are provided, supporting and rigidifying the flexible thin-walled tubular plastic heat exchange member. The plastic heat exchange element defining said plurality of passages is radially expandable by pressure of fluid from said source to avoid scale formation.

Abstract: The process is suitable for detecting leaks in a heat exchanger for heat exchange between two gaseous fluids, for instance for super heating steam. The heat exchanger has a lower pressure fluid circuit and a higher pressure fluid circuit. A predetermined amount of a tracer gas, typically helium, is injected into the higher pressure fluid at the inlet of the heat exchanger and the presence of tracer gas within the lower pressure fluid is determined at the outlet of the heat exchanger. If the lower pressure gas is steam to be super heated, a minor amount of super heated steam is sampled at the outlet of the exchanger and is condensed. Then the uncondensable products are examined for presence of tracer gas.

Abstract: The present invention relates to an automotive air-conditioning system comprising an arithmetic means, control means, diagnostic control means and diagnostic setting means. The invention enables one to diagnose whether output devices such as an air mixing door, a compressor or the like are normally operable or not.

Abstract: A method and an apparatus for closely regulating the temperature of a laboratory reaction vessel arrangement are proposed which permit a desired temperature change to be rapidly established. In the method, a fluid heat transfer medium is introduced into a thermal chamber formed by a reactor vessel and a jacketing vessel of the laboratory reaction vessel arrangement in a finely turbulent and essentially helically ascending manner. In the apparatus for performing the method, a nozzle is provided in the lower region of the jacketing vessel and extends into the thermal chamber for appropriately introducing the fluid heat transfer medium into the thermal chamber.

Abstract: A method for the detection of waterside fouling conditions in plant condensers and the differentiation between types of fouling conditions is described. The operating conditions of a pilot scale condenser are continuously matched to the dynamic operating conditions of a plant condenser and performance features (such as OHTR and pressure drop) are monitored and compared, thereby indicating to the plant operator whether fouling is occuring and, if so, whether there is macrofouling or microfouling.

Abstract: A diagnostic thermostat for a building includes an indoor temperature sensor, an outdoor temperature sensor, and a standard arrangement for cycling a furnace on and off in response to the level of the indoor temperature. A time clock is included and the desired indoor temperature can be set. A microprocessor determines, on the basis of various signals, the heating performance of the building over a given period of time, and this heating performance can be displayed.

Abstract: The invention relates to a cooling device for a multi-stage compressor in which two coolers are placed in a common housing. The two coolers cool the medium of the preceiding stage of the multi-stage compressor heated by the input compressor work. The common housing has chambers that are divided into different pressure stages, are connected to the multi-stage compressor by inlet tubes and outlet tubes, and contain water separators with condensate removal pipes associates with them. To be able to conduct the medium to be cooled with a minimum of pressure drops, dividing walls (13, 23) are provided at a distance from the top and bottom end, respectively, of the cooling housing (50). Each dividing wall (13, 23) forms a cylindrical space (24, 14) with the housing wall (51) and the respective end walls (57, 56) of the cooling housing (50) for the installation of the water separators (15, 25).

Abstract: An indicator device is disclosed for indicating that a heat exchanger has been disassembled, cleaned, inspected, reconditioned and subsequently reassembled and rebrazed. The device includes an elongate housing which defines an inlet and an outlet port. A first and a second tube plate are spaced axially within the housing and a plurality of heat exchange tubes extend through and between the plates. A first seal is disposed between the plates and the tubes for sealing the tubes relative to the plates and a second seal is disposed between the tube plates and the housing for sealing the tube plates within the housing.

Abstract: The invention relates to a boiler for boiling a mash or wort, having an interior partition dividing the boiler into a heat exchanger section and a precipitation section. The boiler according to the invention is characterized in that the partition divides the boiler into an inner precipitation section and a surrounding heat exchanger section, i.e. in that the precipitation section and the heat exchanger section are disposed one within the other. This results in the particular advantage that the overall height of the boiler may be reduced. Since in addition the full height of the boiler is available for the accommodation of pipe conduits in the heat exchanger section, the flow resistance in the pipe conduits may be reduced. In summary, the boiler according to the invention is of simple construction to thereby facilitate the cleaning thereof.

Abstract: An exhaust gas containing sulfur trioxide is passed through a first heat exchanger which cools the gas to a temperature which is above the sulfur trioxide dewpoint, so that condensation of sulfur trioxide does not occur in the first heat exchanger, but below a material limit operating temperature of a second heat exchanger, which further cools the gas below the sulfur trioxide dewpoint, whereby the first heat exchanger is protected against corrosion and the second heat exchanger is protected against thermal damage.

Abstract: Control knob for temperature control switch is provided with means for heating or/and cooling the same, whereby, by feeling of the temperature of the control knob with a finger tip, it is possible to instantaneously identify what the function of the control knob which the finger has toughed is, without turning the sight to a switch, and, even when the shapes and way of disposition of control knobs are identical with one another.

Abstract: An apparatus for moving an object in an isolated environment may be employed as a high pressure and temperature facility for testing steam generator tubes. A tube to be tested extends through an opening in a plate that is mounted in a test vessel. The vessel is partially filled with water having selected contaminants, and heated water under high pressure is circulated through the tube to raise the temperature and pressure within the vessel. A lever arm having an inner end and an outer end extends through an opening in the test vessel. A vibration-coupler connects the inner end of the arm to the tube under test, and a fulcrum-former operationally connects an intermediate portion of the arm to the test vessel. The outer end of the lever arm is connected to a plug element which is shaken, so that the arm pivots about a fixed point at the fulcrum-former and the vibration-coupler moves the tube under test with respect to the plate.

Abstract: A heat exchanger comprises a vertically arranged circular-cylindrical holder closed at its upper end and at its lower end, and a pipe coaxially arranged within the holder. A fin is secured to the inner pipe and consists of a plurality of interconnected lamellae extending radially from the pipe, the fin being helically wound around the pipe so that the adjacent lamellae of successive turns of the resulting helix overlap each other in part, viewed in the circumferential direction of the pipe. A capillary passage is located in each lamella above the surface of an underlying lamella in a position shifted with respect to the capillary passage of the underlying lamella.

Abstract: A temperature control system used in association with a heating and cooling system supplying warm or cool air to a duct system for maintaining accurate temperature in a zone of multiple zones utilizing a microcomputer based thermostat for modulating a damper assembly in the duct system feeding the zone, thereby controlling the volume of air flow in the duct system to the zone to match the load in each zone. The thermostat has a digital readout display thereon indicating the temperature to be maintained in the zone and which can selectively display the duct temperature of air and/or the zone temperature of the air. The thermostat controls a damper assembly which includes a stepper motor for pivoting the damper blade between open and closed positions with the duct temperature sensor located before the damper blade in the duct. Calibration to provide setting of the zone temperature to conform with an accurate thermometer is provided in the thermostat, as well as selectable stop positions for the damper blade.

Abstract: Air drying apparatus wherein input air to be dried is passed through an air tube which contains a smaller refrigerant tube, with precooled air from the air tube being forced by baffles to flow along a tortuous path over the exterior of the air tube. The baffles being truncated discs positioned in the shell so that alternating baffles have the truncations facing in opposite directions.

Abstract: A steam generator wrapper closure and a method of installing the same includes a plug member (108) which includes a large diameter portion (110) and a small diameter portion (112) with an annular shoulder portion (114) defined therebetween. A locking pawl (124) is rotatably mounted upon the plug (108) through means of its shaft (122). A pawl shaft extension rod (154) and a handle (150) are utilized to manipulate the pawl (124) and the plug (108) from a position external to the steam generator outer shell (16). The axis of the pawl shaft (122) is radially offset with repect to the axis of the plug (108), and the diametrical extent of the pawl (124) is less than that of the small diameter portion (112) of the plug (108).

Abstract: A rotary, Perkins tube heat exchanger for processing hot contaminated gas flows emanating from appliances such as laundry driers, grain driers and the like. The case of the heat exchanger is located relative to the rotor so as to lie in the gas flow boundary layer established by the latter. The case is provided with a boundary layer purge port in the hot gas chamber. An airfoil extends inwardly from the case into the gas flow boundary layer. It causes increased local turbulance in the boundary layer gas. It also diverts a predetermined proportion of the boundary layer gas and its burden of contamination products out through the purge port. The boundary layer airflow cleans both the interior of the case and the rotor, even through the rotor is characterized by the presence of a multiplicity of small openings. The device thus is rendered self-cleaning and may be operated for extended periods of time without buildup of contaminants within the heat exchanger case.

Abstract: A system for monitoring energy use by each of a plurality of tenants or other users of energy provided by a common heating/cooling plant and for allocating the energy expense for a building among such users on a pro-rata basis.

Abstract: Apparatus for positioning a probe carried by an elongated flexible carrier includes a cantilevered telescoping extensible boom. A sprocketed tractor feed mounted at the distal end of the boom engages apertures in the carrier for feeding it and deflecting it from the boom in a direction substantially perpendicular to the longitudinal axis thereof. The tractor feed is mounted for rotational movement about the longitudinal axis of the boom. A withdrawal device engages the carrier adjacent to the supported end of the boom for reeling the carrier up into a cartridge. Extension and retraction of the boom is effected by a rack and pinion mechanism. Rotary resolvers measure the movement of the boom, the movement of the carrier with respect to the boom and the rotary movement of the tractor feed for providing signals to an associated microcomputer, accurately to detect and control the position of the probe. The microcomputer additionally provides on-line visualization of sludge profilometry and topography.

Abstract: A low cost automatic ice cube maker of simplified construction for use in the freezer compartment of a domestic refrigerator. The ice maker includes a onepiece, molded plastic bail or sensing arm for monitoring the level of ice cubes in an underlying storage bin. The movable bail includes a fingerlike resilient projection extending radially from one of the end portions of the bail. The distal end of the projection engages a portion of the ice maker fixed in position relative to the movable bail wherein the resilient projection functions as a springlike member biasing the bail toward a lowermost position. The ice maker also includes a pivotally mounted ice tray that can be easily snapped out of its ice making position for removal and cleaning at a location outside the freezer compartment. An externally accessible mechanism for actuating a test switch of the internal control circuit of the ice maker is provided to facilitate servicing of the ice maker.

Abstract: An arrangement for measuring a quantity of heat given off by a heating body to a space and for simultaneously controlling a fluid stream passing through the heating body and serving as a heat carrier for regulating of the space temperature, has a volume stream regulator for allowing a constant fluid stream. An on-off valve is controlled by a signal generator for example a space thermostat via a control valve and switched by the energy of the fluid stream to block or unblock the fluid stream. A temperature sensor cooperating with the heating body and an electronic element determine the quantity of heat by integration of temperature difference values converted into an electrical value during opening times of the on-off valve.

Abstract: The present invention relates to a double barrier heat exchanger between a radioactive primary fluid and a secondary fluid making it possible to detect a possible primary fluid leak in the exchanger. The primary fluid circulates in a primary duct and the secondary fluid circulates in a secondary duct, a junction matrix being positioned between the primary and secondary ducts and in contact with the latter. The matrix is in the form of a compact metallic mass incorporating at least one element, e.g. silver, which can be made raidoactive when it diffuses into the primary fluid. Application is to sampling circuits in nuclear reactors.

Abstract: An electronic temperature controller having a great stability and an improved sensitivity to temperature. The controller is designed to operate at preset temperatures depending on the occupancy and/or the presence of light in each of the rooms of a household. A microcomputer supplies control signals to a heating device until the ambient temperature in the room reaches the appropriate preset temperature. To do so, use is made of an electronic regulator of the proportional-integral-differential type. The control signals of course control the amount of energy (i.e. heat) given off by the heating device in the room. This electronic controller permits to regulate temperature automatically and thus save heating energy when the rooms of the house are either unoccupied or not lit. This electronic controller may also incorporate an electronic thermometer, an alarm system and/or a fire alarm. It may also control any appliance in a room depending on a change in occupancy and/or lighting in the room.

Abstract: A compact secondary heat exchanger, installed in the path of room air through the casing of a gas furnace, utilizes a unitary condensing coil having parallel upper, middle and lower sets of tubes through which the flue gas passes sequentially to a collector manifold, exhausted by a blower. The coil is slanted downwardly from the hot gas manifold. Condensate formed in the first and second sets of tubes flows downward to an intermediate manifold between the first and second sets of tubing, condensate from this intermediate manifold is drained downward to a collector manifold beneath.

Abstract: A heat exchanger with a stack of alternating hollow panels and corrugated plates includes a unique arrangement for positive drainage of water which flows down onto lower headers of the hollow panels as a result of condensation of moisture contained in air, which is pumped through the heat exchanger. A substantially vertical drain channel is defined between facing outer surfaces of the lower headers of nearby hollow panels, so that the water is guided downwardly from the upper surfaces of the lower headers into a sump as well as along the sides of the lower headers.

Abstract: A temperature controller for an air conditioner including a temperature sensor that provides an output temperature from the air conditioning device, and a temperature rate of change comparison circuit for providing an indication signal that the rate of change from the temperature sensor exceeds a predetermined reference rate of change indicating that the rate of temperature change from the air conditioner is less than a reference cooling rate. The indication signal from the temperature rate of change comparison circuit is input to a disabling means that disables the air conditioning device. In an embodiment, the rate of change comparison circuit is connected to the thermostat for the system to sample the air conditioning temperatures for comparison with the reference cooling rate.

Abstract: The shroud is formed from sheet material and is cylindrical in shape. A plurality of spacers are associated with the sheet material. These spacers are designed to engage the outer surface of a duct to hold the cylindrical sheet material in radially outwardly spaced relationship to the duct, defining thereby an insulating air gap between the outer surface of the duct and the shroud. The angular space between the spacers serves as gas channels to permit gas to flow between the shroud and the outer surface of the duct, along the length of the duct. The shroud has a straight axially extending slot along its entire length for easy removal from a duct. An axially extending edge receiving pocket is formed on the shroud adjacent the slot for receiving the adjacent longitudinally extending edge of the slot to hold the shroud in a cylindrical shape and to provide a gas-tight closure for the slot.

Abstract: A method and apparatus for removing moisture from compressed gases such as compressed air, the appparatus being completely self contained and requiring no external power or energy source, nor any source of coolant medium, other than ambient air. The apparatus of the invention comprises a reservoir for containing a volume of liquid, and a heat exchanger connected to the reservoir located beneath the reservoir through which the liquid from the reservoir can circulate. The method of the invention comprises circulating compressed air through the heat exchanger to reduce the temperature of the compressed air and condense moisture therefrom, and circulating water through the heat exchanger from the reservoir to reduce the temperature of compressed air circulated through the heat exchanger.

Abstract: This invention relates to a process for magnetically stabilizing the operation of contactor columns containing immiscible fluids passing in dispersed countercurrent flow. The process operates by including, in an appropriate fluid phase, a magnetizable component in an amount which does not substantially change the nature of the liquid in that phase and, further, imposing upon at least a portion of the column containing dispersed phases, a magnetic field sufficient to result in substantially diminished radial mixing of the phase containing the magnetizable substance and diminished coalescence of the dispersed phase. The phase containing the magnetizable component passes through the stabilized zone in substantial plug flow.

Abstract: A method of removing coatings from scrap glass is disclosed. The scrap glass is milled in the presence of particulate batch, preheated and fed to a glass melting furnace. The particulate batch aids in the milling of the scrap glass. The process removes the coatings from the scrap during preheating and provides clean material for melting.

Abstract: The present invention calibrates air flow controllers by simulating pneumatic signals present in typical heating, ventilating and cooling systems. The controllers receive pneumatic status signals and in response, operate dampers in the air ducts. Each controller must be set to move the damper among positions for air flow rates between calibrated minimum and maximum air flow positions in the duct. The apparatus connects through air piping to the controller to be calibrated. A variable regulator adjusts a supply of constant pressure air to simulate the pneumatic signal from a thermostat while a second variable regulator simulates the differential pressure signal. Gauges register the simulated signals. A third gauge registers the damper control signal generated by the controller. To calibrate a controller, the thermostat and differential air pressure signals are communicated to the controller. The controller dial is then adjusted to provide a pneumatic signal which operates the damper.

Abstract: A method for allocating energy costs comprises sensing a first parameter; comparing the sensed parameter with a selectable value of the parameter; initiating recording of data when the sensed parameter bears a predetermined relation to the selectable value; and recording data corresponding in a predetermined fashion to the quantity of energy consumed. The invention also extends to a system for allocating energy costs as a function of at least one sensed parameter.

Abstract: An improved automatic energy-efficient temperature control system for a room or suite of rooms. This system is used in addition to the normal temperature responsive switch which is used to control a heating and/or cooling unit. This system involves a second temperature sensitive switch, set to a temperature which utilizes less heating or cooling. While using the normal operating temperature while persons are in the room, the second temperature responsive switch is short-circuited by a manual switch, or one operated by a magnetic or gravity means. The control of the shorting switch is made responsive to the entry or departure of persons from the room. Thus while they are present, a more comfortable operating temperature is provided and when they are absent from the room, a more energy-efficient situation is imposed.

Abstract: A method of the exchange of heat between solids where the heated solids are passed through heat conducting tubes defining a first flow path or zone in the heat exchanger and the solids to be heated are passed through the interstitial space around the tubes, or through secondary tubes, in the heat exchanger, defining a second flow path or zone. The solids are physically separated by the walls of the tubes which act as a heat conducting barrier and the solids are flowed, under moving-bed conditions, in counter-current or concurrent directions to enable the heat transfer to be effected.

Abstract: An electric device for monitoring the usage of equipment that is being shared by one or more entities or individuals during a predetermined schedule and that needs to be made available to any one of these entities or individuals outside that schedule. The device includes timing means programmable for any schedule and capable of activating complementary relays, one of them a normally open and the other one a normally closed. The contacts of one of these relays being connected to a suitable point in the equipment being shared so that its operation may be interrupted or turned on. A plurality of second relay means, one associated with each one of the entities, are also connected to that point in the equipment so that each entity may be able to connect the equipment. Also, there is an elapsed time meter associated with each one of those second relay means so that the time that the equipment is used, outside the predetermined schedule, by a particular entity may be measured.

Abstract: A method and apparatus for cooling waste gases of a temperature in excess of 800.degree. C. using radiant heat transfer to a plurality of fluidized beds. Solid particulate material is contained within a housing and divided into a plurality of fluidized beds by baffle means and fluidizing gas injected upwardly through the solids, without transfer of solids from the upper surface of a bed to adjacent beds. The hot waste gas is cooled by radiant heat transfer through the surfaces of the beds. Heated solids are cooled by either flow through the housing and cooling of the same outside the housing, or by coolant passed through heat transfer tubes that are positioned within the beds of solid particulate material.

Abstract: With an air conditioning system a plurality of building areas, for which individual energy accounts have to be rendered, are supplied by a common fresh air supply and cooling installation. The volume flow rates are controlled by one volume flow rate regulator each, the setpoint of which is adjustable through a servomotor. An output signal representing the setpoint of the volume flow rate regulator is generated and is applied to a meter. This provides with sufficient accuracy the distribution of the volume flow rates between the various building areas as a base for the accounting and billing of energy expenses.

Abstract: A system for submetering artificial energy consumption in a multi-user environment in which a single central system source services the several separate users by means of individual space conditioning subsystems is disclosed which enables accurate proportioning of subsystem energy consumption by monitoring the time intervals of the OFF/ON status of each individual space conditioning subsystem along with the temperature of the conditioned space and utilizes the monitored time intervals and temperature in conjunction with the relative heat capacity of each individual conditioned space to determine the heat consumption of each subsystem relative to all the subsystems served by the central source.

Abstract: A method of separating the two exhausts of a low pressure double flow turbine so that the turbine can be directly connected to a zoned or multi pressure condenser having a shell side low pressure chamber with influent cooling water in the tubes disposed therein and a shell side higher pressure chamber with effluent cooling water in the tubes disposed therein and utilizing structural elements within the turbine and baffling to form low leakage seals between the two chambers.

Abstract: The present invention relates to a device for processing a flow of solid products with a counter-current flow of liquid to achieve for example a heat exchange comprising a drum rotating about its longitudinal axis, an endless screw or helix arranged within the drum and solid in rotation therewith, and defining sections, in each section is arranged a vane element which is secured to the face of the drum between two adjacent turns of the helix to impede progression of the products in the drum, and perforations or grids provided in the portion of the helix turn which is located upstream of the vane with respect to the direction of progression of the products in the drum, and above and upstream of the face of the vane, this invention being used more particularly in the food industry.

Abstract: Two parallel heat exchange tubes having that part of a support structure between them to be interrogated for defects. A pair of radiation sources are positioned in the one tube to straddle the interrogated support portion, and a radiographic film is positioned in the tube behind the interrogated portion.

Abstract: Individually useable wave-powered pumping means, solar distillation means, and cyclonic wind generating means, together with a system which employs each of them for harnessing natural energy sources are disclosed. Wave and solar energy, together with Coriolis acceleration are employed in the system which includes a basin for water situated near an ocean, or other such body of water, having a surface subject to wave action. A solar energy trasmitting cover is provided over the basin for solar heating, and evaporation of water contained therein. Vapor condensing means are located adjacent the bottom of the basin, and an upwardly extending inlet conduit, or passageway, connects the condenser to a source of water vapor above the water surface of the covered basin. Cooled air, and distilled water, are discharged from the condenser to a location outside the covered basin.

Abstract: A remote manipulator arm for positioning and operating tube sheet repair tools within a nuclear generator shell. The arm includes a number of arm segments linked serially, each having a remotely-controlled motor to pivot an elbow in the arm segment by way of gears. A mounting bracket passes through a manhole in the generator shell and provides a stable point of connection for the arm, both inside and outside the shell, as well as connections for power and control signals to the arm. A workhead is provided for mounting on the arm end opposite the bracket, and can carry a plurality of tools to conduct repair operations on tubes. The mounting bracket can be installed from without the shell and does not block the manhole, and the arm is self-installing, requiring no human presence within the generator shell.

Abstract: A modular bundle of tubes for a steam condenser comprises two perforated plates (24, 25), a series of tubes (22) interconnecting the perforated plates, and a set of intermediate supporting plates (23) distributed between the two perforated plates. The improvement wherein both perforated plates are the same size, each being surrounded by a reinforcing frame (24, 25) which is thicker than the perforated plate, and wherein drawbars (26) fitted with length-adjusting means (27) interconnect the perforated plates, said drawbars being fixed to said frames and being distributed along the said frames.

Abstract: There is disclosed an energy consumption indicating system for a multi-occupancy dwelling including a plurality of units each having a space heat exchanger and a thermostat and wherein said multi-occupancy dwelling is provided with a main heat exchanger having an outlet conduit, an inlet conduit and at least one circulating pump and wherein a conduit member is provided for each unit in fluid communication to the main heat exchanger and the space heat exchanger in each unit and wherein fluid flow through each conduit member is effected in response to a thermostat in each unit and wherein a time meter for each unit is energized to measure time duration of fluid flow through the conduit member.

Abstract: Exhaust gas treatment method and apparatus extract heat from an exhaust gas by operating in a water-condensing mode which allows more heat to be recovered, removes particulate matter and condensed acid from the exhaust gas, and washes heat exchange surfaces to keep them clean and wet to improve heat transfer. Systems for heating water, air and both water and air are disclosed. Methods of constructing and assembling improved heat exchangers are disclosed.