EP0056399A1 - Modulated temperature control of structures with central heating units - Google Patents

Abstract

Heat-energy transfer control system between a central unit and a structure comprising several spaces. The heat-energy transfer is carried out using one or more heat valves (10) arranged in each space to independently control the speed at which the energy transfer takes place between this space and the central unit (1). The heat valves are controlled to ensure maximum use of the CPU time (tone) while meeting the room or zone temperature requirements: therefore, in normal operation, less of all heat valves (10) are active, the number of these valves in operation corresponding to the capacity of the central unit. The maximum use of the ton time of the central unit is carried out because the use of heat valves (10) makes it possible to regulate the ignition speed of the central burner by the thermal load of the structure. Advantageously, this ignition speed can vary and it is regulated by the same device as that which controls the heat valves.

Description

MODULATED TEMPERATURE CONTROL OF STRUCTURES WITH CENTRAL HEATING UNITS

The present invention relates to heat transfer mechanisms for residences and the like.

The concepts herein disclosed have particular value in the context of steam-heat and hot- water systems in use, wherein a hot fluid from a central heater system is delivered to multiple radiators in a family dwelling, commercial structure, industrial building or the like. Moreover, the present ideas are especially useful in connection with retrofitting activity. In what now follows, the invention is discussed mostly in the context just mentioned, but it is not so limited in scope.

A significant problem with respect to the current fuel situation is the intractability of radiator-heated, centrally-fired, steam and hot-water systems in the northeastern region of the United States where a significant fraction of residences are so heated and the residences often do not lend themselves easily to other solutions (such as insulation). In large, old houses a strategy which has been proposed is that of area (or zone) heating with a lower average temperature throughout the structure. One mechanism proposed to accomplish such area heating is, by way of example, to have liquid or steam valves in the hot water pipes to the radiators, which valves are hand set to effect an area heating approximation. Such valves, however are often difficult to operate and susceptible to failure, and automatically-activated valves (to permit sequencing) are expensive and difficult and expensive to install.

Accordingly, it is a principal object of the present invention to provide a temperature-control system that permits facile retrofitting of existing hot water and steam centrally-heated, structures.

Another object is to provide a temperature-control system that is economical to fabricate, easy to install, yet efficient and dependable. Still another object is to provide a temperature-control system that does not depend on restricting flow of the primary fluid in the heating system.

A further object is to provide a retro fittable system which provides optixaal control of the flow of heat from the central burner to the individual rooms or areas,

A further object is to provide a system which permits the firing rate of the central burner to be matched to the heating load of the structure.

Still another object of the present invention is to reduce the firing rate of the central burner with concomitant reduction in cycling.

Still another object is to provide optimized temperature control for each room or area in the structure.

A further object is to reduce the transfer of heat through the exterior walls and windows of housing. This is accomplished by preventing the convective flow of hot air set up by the normal placement of conventional radiators. A still further object is to prevent or reduce temperature stratification by means of inducing a circulation pattern which releases hot air at the very lowest levels of the room.

A large heat energy expenditure in the usual steam heating system occurs because in such a system the central burner or boiler installed is sized to provide heat energy to each radiator on the coldest days. Hence, the central burner has a firing rate (i.e., rate at which fuel is burned) that is matched to this worst case, whereas the heat load of the house is always much less. Two consequences flow from such operationt burner cycling is greatly increased! as a result stack temperature and stack losses are increased. The present inventor has found that the teaching herein permits as much as a 50% reduction in firing rates below those normally recommended while still satisfying the heating requirements of the heated structure. It has been further found that greatly reduced burner cycling can be effected, that is, the on/off (t_on/t_off) ratio is much higher in the present temperature control system. Ideally the firing rate would be adjustable to be equal to the requirements of the heated structure and the controlled burner would be on, at a reduced firing rate, at all times during the heating season. The present system minimizes the firing rate for any particular structure, and, hence, maximizes the ratio t_on/t_off

An important trend in the United States is that homeowners have tended toward doing much of the work on. their homes, A still further ob jective of this invention is to provide a heat control system that can be installed by a professional, but one that can be marketed in kit form for installation by the user-owner.

These and still further objects are addressed later.

The foregoing objects are achieved, generally, in a method of controlling heat-energy transfer between a central unit and a plurality of discrete spaces, that includes: assigning temperature values to be maintained at each space of the plurality of spaces (preferably, but not necessarily, as a function of time of day): providing a valving mechanism at each space of the plurality of spaces to effect essentially total control of energy transfer be tween the space in which the valving mechanism is located and the central unit, each valving mechanism including a housing and an air-moving mechanism that provides the valving mechanism with a turn-down ratio of at least four to one, said turn-down ratio: being the ratio of energy transfer when the air-moving mechanism is activated to deliver air between the housing and the space and energy transfer when the air-moving mechanism is de-activated: and controlling the energy transfer of each valving mechanism in a way that maximizes t_on/t_off of the central unit, where t_on is the time that the central unit is on and t_off is the time that the central unit is off to minimize cycling of the central unit.

The invention is hereinafter described with reference to the accompanying drawing in which.

Fig, 1 is a diagrammatic representation of a central heating system employing the pre sent concepts and including a plurality of heat valves and a central controller;

Fig. 2 is an isometric view, partly cutaway, showing one form the heat valves of Fig, 1 can take;

Fig. 3 is an isometric view, partly cutaway, of a modified version of the heat valve of Fig. 2, that includes a flap valve to influence heat flow between the heat valve and the surrounding region;

Fig. 4A is a section view taken on the line 4A-4A in Fig. 2 and looking in the direction of the arrows;

Fig, 4B is a section plan view of a modification of the heat valves of Figs. 2 and 4A;

Figs. 5A and 5B are respectively a front view on and a section side view of the flap valve of Fig. 3;

Fig. 6 is a diagrammatic representation of a portion of the system of Fig. 1; and

Fig. 7 is a flow chart showing one form that the functions of the central controller in Fig. 1 can take. In the discussion that now follows, the system shown diagrammatically at 101 in Fig. 1, for purposes of simplifying this explanation, is taken to be one in which heat energy is transferred from a central unit or furnace (the term "central heat exchanger" is also used herein to denote the element 1) 1 to a plurality of spaces or locations 5A...5N in a structure 102 to be heated. Also, the heating system 101 is taken to be a steam system, but it is to be understood, as indicated above and as shown in greater detail later, that the invention is not limited to steam systems nor to systems wherein heat-energy is delivered to the spaces 5A...5N; such heat-energy can be either extracted or delivered according to the present teaching.

The heating system 101 is a simple cost effective optimum transfer control for the centrally-heated structure 102, the central unit 1 at this juncture of the explanation being a central steam furnace 1. A steam furnace, as is well known, includes a burner (called "central burner" herein), a boiler (called "central boiler" herein) and in ternal piping, all of which are embraced by the designation 1 in Fig. 1. A major aspect of the system 101 according to the present teachings is that of minimizing the firing rate of the central burner—without deleteriously affecting the heating comfort within the structure 102, that is, the ratio of turn-on time (t_on) of the central burner to turn-off time (t_off) is maximized by the present invention. It should be pointed out that at the time the burner is fired and for a time thereafter, heat energy is absorbed totally within the furnace. Some time later heat energy is transferred to the spaces 5A...5N. During this transient situation the heat valves 10A...10N (discussed below) may be used to control heat transfer to the spaces 5A...5N at a level that matches the heat energy the furnace is capable of providing. Once a steadystate is reached (i.e., after the furnace boiler and internal piping, and so forth, are up to temperature) the heat energy delivered to the spaces 5A...5N is substantially equal to the heat-energy output of the central burner. Each space 5A...5N contains one or more of the heat valves 10A...10N that receive steam through piping 40A...40N, respectively, and control signals by way of conductors 30A...30N, respectively. Temperature sensors 11A...11N may be used to provide temperature information along respective conductors 50A...50N to a central controller 2 which delivers control signals on a conductor 51 to the central unit 1 and receives control information from the central unit. Let it be considered at this point in the discussion that the central unit 1 simply has on-off control of the burner. This may advantageously be accomplished by connecting a controlled switching means in parallel with the existing thermostat. The controller 2, as later explained, preferably is a microprocessor adapted to receive feedback temperature information on conductors 50A. ,.50N and to provide control signals at 51 and 30A...30N. Typically, the heat energy delivered to the structure 102 by the burner unit 1 is controlled by controlling the on-time of the unit (assuming the firing rate is fixed). In the usual prior art heating system in fact heat delivery to the spaces 5A...5N is controlled in exactly this way. In the present system, however, heat energy delivered to the spaces 5A...5N is modulated and the rate of such delivery is controlled by the heat valves 10A...10N on the basis of appropriate signals from the controller 2, which may also calculate the fuel consumption from the turner-on time. The heat valves, as explained below, serve as heater control means to control independently the rate at which heat energy is delivered to each of the spaces 5A...5N in such a manner that the steam output of the central boiler is equal to the sum of outputs of the heat valves 10A...10N and that the output of each heat valve is adequate to maintain or move to a predetermined temperature each of the spaces 5A...5N independently, it being understood that ordinarily less than all the heat valves, at any instant of time, will be delivering heat energy to the associated spaces. Each heat valve 10A...10N, as now discussed, includes a housing and an air delivery device. Since all the heat valves in any system usually will be identical to one another—or at least similar to one another—either of two variations 10 and 10' described below can be taken to be any one of the heat valves in Fig. 1.

The hear valve 10, as shown in Fig. 2, includes a housing 3, a fan or blower 12A, and baffles 4A and 4B. The heat valve also works well with only one of the baffles. The housing 3 fits over a local heat exchanger (e.g., a steam or hot water radiator) 8 that exchanges heat from a first fluid (e.g., the steam from the central boiler) internal to the heat exchanger 8 and a second fluid (i.e., the air drawn over the radiator 8). The housing 3 acts to restrict the natural convective driving force of the radiator 8 and it serves as an insulator with respect to radiation between the radiator 8 and the space or room within which it is located. In the present system, the flow of heat energy between the radiator 8 and the environment is regulated by causing a directed flow of air into the housing 3 (i.e., the second fluid herein), about the radiator and out into the environment around the heat valve 10, as now explained. As above indicated, the heat valve 10 is fashioned to have a large turn-down ratio, at least about four to one, where the turn-down ratio is the ratio of heat transferred between the heat exchanger 8 and the environment when there is no forced air flow into the housing and when there is such forced air flow. Ideally, the housing 3 reduces the transfer of heat between the heat exchanger 8 and the environment to at least half the heat transfer without the housing. A greater degree of heat-transfer reduction is desirable. The housing performs the required function by reducing the natural convective driving force of the heat exchanger 8 and by reducing direct radiation to the environment. Regulation of heat transfer, according to the present teaching, is accomplished in the heat valve 10 by the state of activation of the fan or blower 12A which serves to draw air from the surrounding environment into the housing 3 through an inlet 6A. As one example, air within the housing is directed by the baffle 4A to move upward in the direction of the arrows labeled 7A, laterally across the top of the heat exchanger 8 to create convection within the heat exchanger, downward in the direction of the arrows labeled 7B, and out to the surrounding environment through the outlet labeled 6B. The present inventor has found that in the absence of baffling there is a thermal short circuit of the heat exchanger 8. Hence, it is vital not only that there be a forced air flow into the housing 3 but also that the air flow within the housing be such that substantial convection occurs in and about the heat exchanger 8 when such forced flow is present! and the air heated and convected from within the convector or heat exchanger 8 is caused to flow out of the housing 3 and into the surrounding environment. There are other configurations which will accomplish approximately the same result, as already discussed. In this way, the flow of heat energy from the heat exchanger 8, and thus from the central boiler, into the space in which the heat valve 10 is located, is regulated simply by activating and de-activating the fan or blower 12A. In other words, it is the forced air flow into and out of the housing 3 (with appropriate direction of air flow within the housing to assure convection) that modulates heat transfer from the convector 8 to the surrounding environment (i.e., one of the spaces 5A...5N in Fig. 1) and heat transfer from the convector 8 is greatly reduced in the absence of such forced flow. Since the heat control system 101 in Fig. 1 contemplates several spaces 5A...5N (typically six to fourteen in a single family residence), heat energy transfer from the central unit 1 can be (and according to the present teaching is) ultimately determined by the rate of heat-energy transfer from the various heat valves 10A...10N and these are turned on and off according to a predetermined algorithm by signals from a microprocessor in the controller 2.

Several radiators may be left uncontrolled, provided that more or less continuous heating of the spaces in which they are located is desirable. In addition, a number of the radiators in a typical house may be permanently disconnected or turned off when the system described is intalled. This is at least partially because of the increased rate of heat-transfer made possible by the forced convection induced by the fans. An additional point must be made about the disposition of baffles described above. Since the heat valves are to be used in spaces normally occupied by humans, and indeed, in the case of a residential application, where people sleep, it is necessary that the fan means be quiet. By providing a long, wide, obstruction free channel leading to the fans, by directing the output of the fans outward past the screens required by safety regulations, and by locating the fans in the narrowest dimension of the enclosure, noise may be minimized.

It is also desirable to insert an insulating means between the radiator and the exterior wall to reduce the transfer of heat through that wall to the exterior where it is lost. Without such insulating means, heat transfer to the exterior would be enhanced. In the course of development of the present invention, it has been found particularly advantageous to use a foil-covered cardboard or pulp-board to serve this function, to attach a piece of wood to said foil-covered board, and to attach the baffle required for noise reduction and proper flow of air to this wood, so that the combination of the foil- covered board and the baffle form an "L" ; see the L-shaped element labeled 28 in Fig. 4B. The exterior cover or housing 3 may then be pressed against the deformable baffle to create the obstruction-free channel or passage required for noise reduction and optimum air flow characteristics, By suitably locating the air intake and omitting the second baffle, access to the radiator control val-ve (normally provided in an existing system) may be obtained without impairing system operation and the cost of the enclosure may be minimized.

The housing 3 may be constructed either of wood or wood products, or may use a skin and frame construction with an air apace provided between the skins (or an air space filled with some light material). For reasons of weight and economy, the use of metal is believed undesirable, though it is feasible from an engineering viewpoint. Since the flow of heat into the each room or area is controlled by the state of activation of the fan, the relative proportions of heat delivered to each area may be calculated readily by the central microprocessor. This may be used to provide an allocation and control of heating costs to individual apartments in a centrally heated apartment building. It is desirable to line the housing with a reflective material such as, an aluminum foil.

In the present system the heat transfer from the radiators 8 is cycled—not the central burner. Such arrangement permits use of much lower firing rates (down as much as 50% of normally recommended) while satisfying the heating requirement of the structure 102; studies have shown that a reduction of at least 25% in fuel use (and estimates go as high as 40%) can result from a properly designed system 101. Before detailing the precise approach for the controlling energy transfer, it may be useful to mention, for emphasis, the importance of such control in the context of energy saving. The electrical circuitry of Fig. 1 is shown in Fig. 6 for purposes of the explanation below with respect to Fig. 1, it being noted here that the connections 30A...30N can be accomplished along the ac lines labeled 15A...15N, respectively. In other words, on-off signals to an on-off switch within each of the blocks 12A...12N can be carried by the 120 volt ac conductors that carry electrical power to the respective fan or blower 12A... (see United States Letters Patent 4,070,549). When heat is called for by signals to the controller 2 from the various room (or space) temperature sensors, the controller 2, along a multi-conductor 51, determines the temperature of the water (either directly or from its past firing history) in the central unit or furnace 1. If the temperature there is below some predetermined value, the unit 1 is fired and shortly thereafter some of the fans or blowers 12A... are energized, the number being matched to the central heating unit 1 such that the heat extracted by the combined heat valves 10A... matches the heat input to the system by the central boiler. In this way the ratio t_on/t_off of the central burner is maximized. Let it be assumed, for example, that the structure to be heat controlled is a sevenroom house. Each room is assigned a temperature level for different times of the day. The controller (e.g., a micronrocessor) scans the temperature values over inputs 50A...50N in Fig. l! assume all the rooms are below temperature. Signals move between the controller 2 and the central burner unit 1, the fans or blower 12A...12N and the temperature sensors 11A...11N. At this juncture the controller makes a number of decisions in accordance with a pre-established pattern which may be of the type shown in Fig. 7 which is an exemplary flow chart for the microprocessor. Typically, the fans or blowers 12A...12N in three to four rooms will be energized in some pre-arranged schedule until all rooms in the house come up to temperature. In this way the firing rate of the central burner is minimized, as is, also, cycling of that central burner, and the temperatures within the rooms are determined by the heat valves—rather than the central unit—on the basis of user supplied information to the controller 2. The control pattern in Fig, 7 is based upon a closed- loop control system.

The central controller should be adapted to control the burner and the heat valves so that, over the period of a day, the temperature in each of the rooms or areas most closely approximates the desired temperature for such time of day. To illustrate this point, consider the case of a room which is supposed to be at 60°F at 5p.m. and at 70°F at 6ρ.m, The room cannot be warmed up instantaneously. On the other hand, any control algorithm employs a series of trade-offs resulting, at any given time, in rooms being hotter or colder than the precise set temperature. By "looking ahead," the direction of the "errors" can be made to be consistent with the future desired temperature. Likewise burner control decisions may be impacted by a consideration of future desired temperature settings. A more sophisticated control scheme allows for the consideration of variables such as outside temperature and the rate of change thereof and the requirements for domestic hot water for those systems that heat domestic hot water in the central heating system. An open-loop system can also be used, as now explained.

In the open-loop system, the user again establishes the temperature for each room. There is only one temperature sensor in one roomi the temperature in the other rooms is maintained on the basis of experience. The length of time each fan is allowed to be on in each room is set to be a function of the time required to heat the room with the temperature sensor, the desired set temperature of each other room. An experimentally used open-loop algorithm found to give reasonable results is presented below.

The user sets the desired temperature for each room in degrees Fahrenheit. The microprocessor subtracts 60 from the number entered, calling all results less than zero equal to zero and all results greater than 20 equal to 20, If the temperature sensor is below the set temperature of the controlled room, a heating cycle is begun. During this cycle each fan is turned on for a number of minutes equal to the result of the subtraction described above, A fixed percentage of radiators are "on" at any instant in time. A cycle is completed when each radiator has been turned "on" and then "off."

At this point, a check is again made to see if the controlled room still requires heat. If so, a new cycle is initiated. If the controlled room no longer requires heat, the central burner is turned off—but at least one additional cycle is performed to extract the heat remaining in the system. This algorithm may be modified for maximum performance by making the percentage of radiators turned "on" a function of the past operating history of the central burner--i.e., if the burner has been off for a protracted period the initial "on" percentage should be low (and possibly zero) and increase with each cycle.

The baffled heat valve 10 of Fig. 2 may be replaced by the heat valve designated 10' in Fig. 3 wherein a flap valve 13 replaces the baffles 4A and 4B in Fig. 2. As shown in Figs. 5A and 5B, the flap valve 13 has a flap 18 that opens, i.e., pivots counterclockwise in Fig. 3 and clockwise in Fig. 5B, to permit air to flow into the housing labeled 3A and over the top ^f the radiator 8, again to avoid a thermal short circuit which occurs if the incoming air were directed, for example, below the radiator 8 between input and output of the housing 3A.

The housing 3 or 3A, as shown in Fig. 4A_» can be fabricated of fiberboard which serves as a the-qmal insulator. The top and sides of a housing can be secured together by screwing each into a wood strip as shown. A weather stripping 23 and foil 24 serve to insulate the interior of the housing against heat transfer to a wall surface 25 or the room area. The numerals 26 and 27 represent respectively the floor and walls of the room being heated.

The foregoing explanation is made with reference to a system wherein the first fluid, i.e., the fluid within the radiator 8, is a vapor (steam), but the system 101 in Fig. 1 can be a hot-water system with results at least as good as derived from a steam system. Furthermore, the central unit can be or can include a cooler (i.e., an air conditioning unit); in this case the first fluid will be cooler than the second fluid and heat valves 10A...10N will cool the structure 102. The design of the heat valves must now be reversed, as would be obvious to one skilled in the art. Again matching the heat transfer to the structure 102 to the capacity of the air conditioning unit results in large energy savings, as is known, The temperature sensors 11A...11N may be temperature-to-frequency converters, for example, with a phase locked loop being used as a detector. In such an arrangement, the variable frequency signal can be transmitted over ac building wiring and the phase locked loop would be located in the controller 2. The temperature sensing means can provide a signal which is converted to a coded sequence of digital pulses for transmission over the ac wiring (or multi-component lines). A microporcessor in the block 2, in addition to the functions above described, can provide information on firing rates, room heat requirement, and so forth. The microprocessor transmit/receive unit may be a chip similar to GI AR-38470 or GI AR-38475 marketed by General Instruments, or it may be a general purpose microprocessor which also performs the transmit/receive function. These chips can be programmed to provide the above-mentioned functions and other functions can be easily provided, e.g., input data to the controller means can include the outside temperature or the need for domestic hot water and these data can be factored into the decision-making process. In the controller 2, batteries may be supplied to protect against ac system outages and crystal-controlled timing may be used.

The present system permits active management of heat transfer to, among other things, free the firing rate and cycling of the central unit—whether it be a heater and/or cooler, e.g., a heat pump—from pulsed requirements thereby, for this reason alone, giving substantial savings. It permits a reduction in window losses (due to altered air circulation patterns) and other losses as well as reduced stack (and other transient) losses and lower stack temperatures. Zone heating control is greatly simplified and the equip ment is simple to install, low cost, reliable, easy to repair, and retrofittable. The system permits use of readily available materials which can be marketed in kit form for installation by the user in existing central heating systems. Furthermore, the forced convection enhances heat transfer from individual radiators to the surrounding region and acts to reduce stratification and favorably alter room air circulation patterns. Efficiency can be enhanced by having continuously- variable central burner or a multi-level firing rate. In this situation, control of the firing rate of the central heat exchanger may be effected in part, by using a multi-speed forced-air burner with higher speeds corresponding to rarely used but less efficient modes of operation.

The heating system may also be a hot air system, in which air is heated in a central heat exchanger and delivered to the various spaces by ducts. In this case, the advantages described may be achieved by remotely controlling the flow from the ducts on a room-by-room basis. The same principle, of course, may generally be applied to a central air-conditioning system, as previously indicated.

The foregoing and other modifications of the present invention will occur to persons skilled in the art and all such modifications are deemed to be within the scope of the invention as defined by the appended claims.

Claims

What is claimed is: 1. For use in a heat-energy transfer system wherein energy transfer is between a central unit and a plurality of spaces in a structure comprising a multiplicity of such spaces each space of the plurality of spaces having a local heat exchanger located therein to receive a fluid from the central unit and to exchange energy between the fluid and the associated space, energy valving means for installation in each said space which is activated and de-activated to control energy transfer between the central unit and the space in which particular energy valving means is located, comprising a housing adapted for installation over and about the heat exchanger in each said space operable to effect a large turn-down ratio on the associated heat exchangers, wherein the turn-down ratio is the ratio of heat transferred between the associated heat exchanger and the surrounding environment when the energy valving means is energized and de-energized, respectively, said energy valving means further including air moving means operable, when activated, to direct air with respect to the associated heat exchanger in a manner that greatly increases the energy transfer between said associated heat exchanger and the environment, essentially total control of energy transfer between said associated heat exchanger and said environment being accomplished by energy the valving means.

2. Apparatus as claimed in claim 1 in which said turn-down ratio is at least four to one.

3. Apparatus as claimed in claim 1 in which the central unit is a furnace, in which the associated heat exchanger receives a hot fluid that serves to heat the air drawn over the heat exchanger by the air moving means associated therewith, the air moving means being operable to create an air circulation pattern that minimizes by-pass of the associated heat exchanger and directs hot air into the space at a low level to reduce temperature stratification.

4. Apparatus as claimed in claim 1 that includes controller means operable to permit selective transfer of energy between the central unit and said spaces at a level that matches the capability of said central unit to maximize the ratio ^^/^off» wherein t_Qn is the on time of the central unit and t_off is the off time of the central unit,

5. A system to control temperature in a structure comprising a plurality of individual spaces, each space of the plurality of individual spaces having disposed therein a heat exchanger connected to receive a first fluid from a central system and adapted to exchange heat energy between the first fluid internal to the heat exchanger and a second fluid external to the heat exchanger, that comprises; a heat valve comprising a housing adapted to enclose the heat exchanger located in an associated space and fluid moving means which when activated is operable to direct the flow of the second fluid relative to the heat exchanger in such a way that there is no substantial natural convective driving force with respect to the heat exchanger in the absence of a flow of the second fluid into the housing effected by action of the fluid moving means but there is substantial convective driving force effected by flow of the second fluid with respect to the heat exchanger when the fluid moving means is activated in order that energy flow between the heat exchanger and the space within which the heat exchanger is located is essentially controlled by the fluid moving means, and means to control the operation of said heat valve.

6. A method of controlling temperature within certain spaces in a structure comprising a plurality of discrete spaces, that comprises) assigning temperature values to be maintained at each space of the plurality of spaces as a function of time of day; providing a heat valve at each said space of the plurality of the spaces to deliver and control transfer of heat-energy to the space in which the heat valve is located, each heat valve having a heat exchanger, an enclosure about the heat exchanger, the enclosure being operable to inhibit natural convection with respect to the heat exchanger and an air-moving mechanism to deliver air into the enclosure to effect forced convection about the heat exchanger to provide the heat valve with a turn-down ratio of at least about four to one, said turn-down being the ratio of heat-energy transfer to the associated space when the air-moving mechanism is activated to deliver air into the enclosure and from the enclosure to the space and heat-energy transfer when the air-moving mechanism is de-activated, and controlling the air-moving mechanism in each said heat valve to maintain the temperature in the associated space, in accordance with a predetermined pattern in which less than all the air-moving mechanisms are energized at any instant of time.