Heating system with reserve thermal storage capacity

A space heating system having a low inertia (low mass and low water content) boiler and a larger heated water storage tank providing a bank of hot water (hereafter called the heat bank) and a "fly-wheel" effect. This provides a thermal bank or load leveler. The temperature of the water in the tank controls "on-off" operation of the furnace of the boiler. The heat sensing means for the heated space controls only the operation of the circulator in the system. A plurality of zones with a common return may be used. The flow rate from the boiler into each of the zones is controlled to be less than the rate of flow from the boiler to the heat bank so that its stored supply of heated water may be quickly established. A domestic water heating coil may be mounted in the heat bank. The connection from the boiler to the heat bank is preferably to the top of the tank which forms the heat bank. The connections to the domestic water heating coil are also preferably at the top of the heat bank. The means for sensing the temperature of the water in the heat bank is preferably associated with the bottom area of the heat bank. In addition, the system lends itself for use with a solar heat source for supplementary heat input.

The present invention relates to heating systems and more particularly to 
heating systems using a heated water storage device which serves as a heat 
bank for heated water and which is used in addition to and in conjunction 
with a low inertia boiler, that is, a boiler having relatively small mass 
and small water content. Essentially the present invention utilizes the 
stored or banked heated water to work as the equivalent of a fly-wheel in 
the heating system to stabilize the boiler operation in relatively long 
operating cycles despite the small water content of the boiler itself. 
BACKGROUND OF THE INVENTION 
A large number of short cycles, occurring especially with zoned heating 
systems, will result in carbonizing the heat transfer surfaces of boilers; 
and as the heating season progresses will substantially increase the 
resultant output of pollutants, increase the flue temperature and reduce 
the boiler efficiency. 
The objective of the invention is to attain 15-30% reduction in energy for 
providing heating and service hot water in buildings which use oil or gas 
as a fuel and hot water as the heating medium. 
A further objective of the invention is to reduce the emittance of 
pollutants from such heating plants up to 90%. 
The above objectives are obtained as follows: 
1. By providing means to prevent short cycling of the boiler required for 
the heating system and to operate it with close to steady-state efficiency 
rather than with the much lower intermittent efficiency. This also reduces 
emission of pollutants which is a function of the number of firing cycles. 
2. By providing means to transfer fuel energy to the heating medium in 
minimum space with minimum mass (low inertia), which reduces the energy 
required for heat-up and minimizes cool down losses. 
3. Providing means to heat service domestic hot water from the same boiler 
which provides heating, without the necessity of maintaining boiler 
temperature throughout the year or without requiring a separately fired 
hot water heater. This reduces flue and standby losses and eliminates a 
separate pilot flame. 
4. Providing means for efficient transfer and control of energy to the 
space to be heated which includes individual zone valves operated by 
temperature sensors, flow control valves and low water content radiators. 
Automatically fired oil or gas boilers operate essentially intermittently 
with the number of firing cycles depending upon the boiler size, climactic 
conditions and temperature controls employed. While energy saving zone 
controls have found wide acceptance in the art, their application also 
contribute to a considerable increase in firing cycles and thereby offset 
some of their benefits. A modern zone-controlled residential hot water 
heating system in a 5000.degree. day area might cycle from 20-30,000 times 
during a heating season and considerably more if, as is frequently the 
case, the boiler is oversized for the installation. Such intermittent 
firing reduces the boiler efficiency from 10 - 40%. With "on" cycles of 
less than four minutes oil burners have been found to operate at an 
average efficiency of only 45 - 50% as compared with their steady state 
efficiency of 75 - 80%. 
Aside from reducing the thermal efficiency, short cycling greatly increases 
the output of pollutants, especially with oil firing, which in turn 
carbonizes the heat transfer surfaces of boilers decreasing their 
efficiency as the heating season progresses. 
Research conducted by the National Air Pollution Control Administration has 
demonstrated that the most serious air pollutants from stationary sources 
result from fossil fuel burning boilers and furnaces; the conclusion 
reached is that intermittent operation of residential heating systems and 
many commercial systems create cyclic peaks of carbon particulate, 
hydrocarbon and carbon monoxide mixtures. These peaks can more than double 
the output of total pollutants that would result from continuous 
operation. 
While the undesirable effects of short cycling have long been recognized in 
the art, so far no satisfactory remedy has been found. 
Large heating installations frequently employ modulation of the firing rate 
of the boiler or the modular concept of step firing a number of smaller 
boilers to meet the fluctuating heating demand. Such systems involve 
complexities, are only partially effective and are not practical for 
residential installations. 
Another approach to overcome short cycling is to considerably increase the 
water content of the boiler itself which will enable it to meet short 
heating demands without firing. Such an arrangement involves however, 
greatly increased flue losses and the necessity to maintain boiler water 
temperature throughout the heating season. 
The invention resolves the problem by providing additional storage of 
heating water in a separate well insulated tank outside the boiler itself 
which is connected in parallel with the heating zones and acts as a load 
leveler (hereinafter called "heat bank") for the heating system. It banks 
heat received from the boiler which can be withdrawn by any of the heating 
zones on demand by the temperature operated zone valves, which in contrast 
to conventional systems energize only the circulator to withdraw heated 
water from the heat bank. When 30% of the heat has been withdrawn from the 
heat bank a wide differential temperature sensor in the thermal bank calls 
in the boiler which now replenishes the withdrawn heat from the heat bank 
and simultaneously supplies the heating system itself. In this manner, 
long operating cycles with steady state efficiency are obtained for the 
boiler. 
By reducing the short cycling of boilers to less then one tenth that of 
conventional systems, the present invention, in addition to increasing the 
efficiency of the operation, will thus reduce air pollution to leass than 
ten percent of the conventional system. 
BRIEF DESCRIPTION AND OBJECTS OF THE PRESENT INVENTION 
The present invention contemplates the utilization of a heat bank which is 
preferably closely coupled with a low inertia hot water boiler employing a 
low water content and high capacity heat exchanger. By closely coupling 
the boiler with the heat bank and locating the circulating lines under a 
common well insulated housing, the standby losses of the complete device 
can be kept below one percent of the boiler input. 
The heat bank of the novel system of the present invention is thus a 
non-fired low pressure insulated storage tank directly connected to the 
heating system which may store (for residential purposes) 20 to 30 gallons 
of water at approximately 200.degree. F and correspondingly larger amounts 
for commercial installations. This stored or banked heat is transferred 
either to the heating system by mixing it with the return water or through 
a high performance built in copper heat exchanger to the domestic water 
circuit. When approximately 30 percent of the stored heat has been 
withdrawn the boiler will be operated until all heat withdrawn from the 
heat bank has been replenished. In this way long operating cycles with 
maximum efficiency are obtained for the furnace in contrast with other 
systems where the boiler is either operated by room thermostats, or 
maintained at operating temperature throughout the period of service. In 
the system of the present invention the boiler is always operated by a 
control which senses the temperature of the heat bank. 
By storing the heat bank eliminates wasteful short cycling and the control 
system thus assures boiler "on" cycles of 8 minutes or more. Further, by 
not maintaining the temperature of the boiler per se, rather, by utilizing 
the hot water from the heat bank, flue losses are greatly reduced. By 
using the stored heat to supply domestic hot water, separate water heaters 
are eliminated. This further reduces energy requirements by eliminating 
flue and stand-by losses as well as pilot flame losses. 
With fewer firing cycles the carbonizing of heat transfer surfaces by 
combustion products in oil fired boilers is greatly reduced assuring 
maximum seasonal efficiency. The combined fuel saving will range from a 
minimum of ten percent when replacing gas hot water heaters to 30 percent 
when replacing tankless coils in oil boilers. 
The heat bank may be utilized in connection with existing heating systems 
and requires no special controls other then those zone valves which may 
already be in the system; and requires no extra circulators or relief 
valves. 
The utilization of this heat bank will also permit a reduction in boiler 
capacity by about ten percent because no allowance need be made for 
pick-up losses simply because the heated water is already stored in the 
heat bank. The oversizing of oil burners and of boilers with tankless 
coils for the purpose of meeting hot water requirements is no longer 
necessary. By storing only inert boiler water under 30 pounds maximum 
pressure, corrosion problems and the need for 100 pound ASME constructed 
tanks are avoided. By eliminating the firing equipment of the conventional 
water heater for domestic water, potential trouble sources are reduced. In 
the event of a temporary furnace breakdown, all the heat stored in the 
heat bank can be transferred to the heating system assuring the home owner 
of extended freeze-up protection. 
The primary object of the present invention is the provision of an 
additional high inertia heat storage container or heat bank for a heating 
system, in addition to the boiler, wherein the heated water to be provided 
for a heating system will be drawn from the heat bank or in combination 
from the heat bank and the boiler and wherein the operation of the system 
will be responsive only to the temperature condition of the water in the 
heat bank rather than to the space heating requirements. 
In the usual hot water heating system the space temperature condition 
signals the operation of the circulator and of the boiler in order to 
provide sufficient heated water to meet the heating demand. Consequently, 
the furnace is turned off and on at very frequent intervals; in a normal 
heating system, this may result in more than 20,000 firing cycles in a 
season. 
A further object of the present invention, therefore, is the arrangement of 
the heating system so that the heat sensors in any particular areas will 
signal the operation of the circulator which draws water from the heat 
bank which thus acts as the fly-wheel in the system. When the temperature 
of the water in the heat bank drops to a predetermined level then the 
boiler is turned on to assist in meeting the demand for space heating, and 
to replenish the heat loss in the heat bank. 
In this simple manner, long, efficient operating cycles replace inefficient 
short cycles resulting from controlling the boiler directly from the space 
temperature sensor.

Referring first to FIG. 1 which diagrammatically shows the structure of the 
present invention, the heat bank 10 is connected by pipe 11 to the return 
12 of the heating system which in turn is connected to the circulator 13. 
The circulator 13 is connected by pipe 14 through the low inertia boiler 
15 to the boiler riser 16. The low inertia boiler 15 may be provided with 
an appropriate gas or oil burner 20 and operating controls in order to 
heat the water in low inertia boiler 15. The water from boiler 15 in riser 
16 is then divided between riser 22 for the heating system and pipe 23 
leading to the heat bank 10. The relationship between the diameter of pipe 
23 and flow controls F is such that the pressure drop across pipe 23 
permits flow through the heating system. As an example, pipe 23 may be 
sized to pass 5 to 6 gallons per minute; flow control valves F may be 
adjusted to pass 2 to 3 gallons per minute. 
The water introduced into the heat bank 10 through the conduit 23 is 
boiler-heated water. When the boiler is operating, the operation of 
circulator 13 introduces the water into the top of the heat bank 10 while 
at the same time providing the pressurized flow down past the hot water 
exchange coil 30 and its elements which will be hereinafter described. 
The riser 22 is connected through the various zone valves Z to the various 
zone risers 32,33 and through the flow regulators F to the radiation units 
40. 
The operation of the circulator is primarily controlled by temperature 
responsive devices located in the various areas served by the various 
radiation devices 40. In contrast with prior systems the burner 20 and 
boiler 15 are not directly regulated by the temperature responsive devices 
associated with the radiation devices 40 or with the room or area in which 
they are contained. The return pipes 41 of the various zones all are 
connected at their output end to the return pipe 12 which as previously 
described is connected through the circulator 13 into the system. 
The circulator 13 forces water through the boiler 15 and the pipe 23 and 
into the heat bank 10. If the zone valves are open, water will also be 
forced through riser 22 into the heating system. The burner 20 and the 
circulator 13 operate under the control of the thermosensitive operating 
control 50 located at the lower end of the heat bank 10. This control may, 
if desired, be exterior of heat bank 10 and in conductive contact 
therewith; or it may be immersed in heat bank 10. When a preselected 
temperature of, for instance 200.degree. F, is reached and no room 
temperature sensor calls for heat, then the control 50 will open a circuit 
as hereinafter described to the circulator 13 and the burner and control 
20 to halt the operating of the burner and circulator. On heat demand from 
any area occupied by one of the radiation units 40 the corresponding zone 
valve Z and the circulator 13 will be energized supplying heat to that 
zone from stored water in the heat bank 10. When water at the lower end of 
the heat bank 10 drops in temperature to 170.degree. F then the operating 
control 50 will close the circuit to the burner 20 and circulator 13 which 
will now operate to supply heat to that particular zone or zones and to 
the heat bank 10 unit until the lower end of heat bank 10 again reaches 
200.degree. F. It will be noted that with the lower end of the heat bank 
10 at 200.degree. the upper end will be at a high level of the order of 
approximately 220.degree. F. The control 50 is provided to turn off the 
burner should temperature in the boiler riser 16 exceed a predetermined 
limit. 
For domestic hot water the cold water input enters through pipe 60 into the 
heating exchanger 30 immersed in the heat bank 10 and the heated water 
exits through the pipe 62 to provide domestic hot water. The thermally 
responsive control member B on the hot water line 62 will close the zone 
valves Z when the temperature of the output water drops below 140.degree. 
(by way of example) giving priority to the domestic hot water supply. 
There is enough inertia in the heating system and radiation units 40 so 
that this may occur without noticeable decrease in space heating. Hot 
water control C will energize the boiler and circulator on prolonged 
demand for hot water before control 50 becomes operative to maintain 
domestic water temperature. 
With average residential installation, the flow regulators F limit the 
water flow in each zone to the order of 2-3 gallons per minute and thereby 
assure that enough pump heat is available for circulation through the pipe 
23 and into the heat bank 10. In this case, the rate of flow through pipe 
23 can be of the order of four to six gallons per minute. 
Referring now to FIG. 2 there is shown a more complete flow diagram for a 
residential heating system operating in accordance with the present 
invention. The water in the system is heated by the burner 20 and the 
boiler 15 and provides heated water to the boiler riser 16. The pipe 23 is 
provided with a reverse flow check valve 24 and introduces the hot water 
into the top of the heat bank 10 which holds the stored or banked supply 
of water as previously described. The riser 16 is connected to a zone 
valve system 16a comprising a plurality of zone valves Z each for a 
particular zone and individual risers 32, 33 for the various zones. The 
zone valves Z respond to thermal conditions in the particular zone area in 
a manner well known, opening or closing the zone valves in order to 
provide heat. As indicated, a room thermostat 70 is connected by a low 
voltage wire 71 to operate the particular zone valve Z for the particular 
zone. All of the elements of FIG. 2 have been given the same reference 
numbers as in FIG. 1 to indicate that the diagrammatic showings are of the 
same device. 
A heat exchanger 30 for domestic hot water is located in the heat bank 10, 
as previously described in connection with FIG. 1; the intake of cold 
water enters through the pipe 60; the heated water exits through the pipe 
62. An appropriate mixing valve 73 may be provided between pipe 60 and 
pipe 62 which may be adjusted as desired to mix appropriate proportions of 
cold water with the hot water in the pipes 62. 
The leads 71 are also connected to operate the circulator 13 in response to 
the call for heat from the particular zone. The control member 50 
responsive to temperature at the bottom of the heat bank 10 will be 
operated at a predetermined low temperature in order to energize the 
burner and circulator and thereby heat the water in the boiler when a low 
temperature is reached. Similarly, the thermostatically responsive device 
B will respond as described in connection with FIG. 1 to close zone valves 
Z when the domestic hot water temperature drops below the desired limit. 
Control C will energize burner 20 and circulator 13 of prolonged hot water 
demand. 
Referring back to FIG. 1 the heating exchange coil 30 is so located in the 
heat bank 10 that it receives the hottest water through pipe 23 from 
boiler 15 and may even be shrouded by a steel tube 75 in order to ensure 
that the hot water entering into the heat bank 10 will be forced over the 
exchanger or coil 30 to obtain maximum heat transfer. 
In FIGS. 1 and 2 the system has been illustrated diagrammatically. 
FIG. 3 shows one form which the basic elements of an oil fired system may 
take. The low inertia boiler 15 is a coil around the burner nozzle and 
combustion chamber 103. The burner 20 is provided with the burner nozzle 
102 which ejects a stream of ignited fuel inside the combustion chamber 
103. The hot combustion gases are targeted toward the ceramic deflector 
104 and deflected upwardly past the coil 15, which forms the boiler to the 
exhaust flue 18. The boiler 15 is a low inertia boiler because it has a 
relatively small volume, -- in this case in the form of a coil around the 
combustion chamber 103. The wall of the combustion chamber 103 is itself 
heated by the fuel so that it will impart heat to the surfaces of the 
turns of boiler 15 by direct radiation while the heated gases deflected 
from the deflector 104 will rise and also heat by conduction of coil 15. 
The heated gases will exhaust through flue 18. 
The boiler 15 is connected to the boiler riser 16 which is thereafter 
connected in the manner described in connection with FIGS. 1 and 2 to the 
various elements of the system. The boiler riser 16 may also have 
connected thereto a pressure gauge 105 and the safety valve 52. The 
circulator 13 is connected to the pipe 14 leading to the intake of the 
boiler 15 at its lower end. Pressure fluctuations may be absorbed by 
expansion tank 107. The output from boiler riser 16 is also connected by 
pipe 23 to the input at 23a for the heat bank 10. Check valve 24 inserted 
in pipe 23 prevents gravity circulation between heat bank 10 and boiler 
15. 
Performance of this system has been tested over extended periods in a three 
bedroom residence with six zone valves and baseboard heating; domestic hot 
water was provided by 40 gallon electric water heater and alternately by 
the system herein shown in which the heat bank 10 was provided with a 30 
gallon storage capacity. A standard circulator 13 provided circulation 
through the heating system. For experimental purposes, heat bank shut off 
valves, arranged between the boiler and the heat bank 10 permitted the 
system to run in the conventional manner and, alternatively, with the heat 
bank 10, to afford a direct comparison of the boiler performance under 
essentially the same heat load. 
Chart 4a is a recording of the boiler and circulator "on" time with one 
zone calling for heat at an outside temperature of 40.degree. F; the 
system here used was the conventional control method where the thermostat 
energizes the zone valve, boiler and circulator. The heat load represents 
less than 10 percent of boiler capacity; the small water content boiler 
reached the high limit of thermostat setting of 200.degree. on the average 
within two minutes while the circulator continued to run as long as the 
zone demanded heat. 
During the test period of 62 minutes (the chart of FIG. 4a) the boiler 
cycled 15 times in an average cycle of the order of 2-3 minutes and a 
total "on" time of 35 minutes. 
The system was then operated with the heat bank and controlled so that the 
room thermostat only energized the circulator; and the burner was 
controlled by a thermostat close to the lower edge of the heat bank 10. 
The heat bank thermostat was arranged with a wide differential making 
contact at 170.degree. and opening at 200.degree.. The boiler thermostat 
was set to open at 220.degree.. 
Chart 4b shows the one hour performance under these latter conditions. At 
the zone thermostat called for heat, the circulator was energized and 
withdrew heat from the heat bank 10 for 41 minutes (period A-B) reducing 
the heat bank 10 temperature from 200.degree. to 170.degree. which 
represents the delivery of approximately 7200 b.t.u. to the zone without 
firing the boiler. When the temperature in heat bank 10 reached 
170.degree., the thermostat energized the burner at point C and caused the 
system to reheat. At the point marked D on chart 4b the zone is satisfied 
but the boiler continues to charge the heat bank 10 until it reaches 
200.degree. at the point marked E. Thus, the heat bank system accomplished 
the same heating performance with a single operating cycle of the boiler 
and a total "on" time of 21 minutes. This represents a fuel saving during 
the test period of 40 percent. 
This experiment therefore indicates that under short cycling the boiler 
efficiency drops to 45 percent as opposed to the much higher steady state 
efficiency obtained with the present invention. 
The heat transfer from water in the heat bank 10 to the domestic water 
supply is accomplished with a finned copper coil 30 of FIG. 3 shrouded by 
a long cylindrical tube 75 extending the full length of the tank. The 
circulator head is used to force the boiler water over coil 30, ensuring 
maximum heat transfer to the domestic hot water system. 
Drawing of hot water will not cause either the boiler or its circulator to 
operate on draws of less than 5 to 8 gallons. Thereafter, a steep 
temperature drop near the bottom of the heat bank will close the 
thermostat 50 and will energize the burner 20 and circulator 13; the 
system will then operate as a forced flow heated water supply producing a 
prolonged supply of domestic hot water at relatively stable temperature. 
The operation is graphically shown in FIG. 5 which shows a comparison of 
hot water delivery from a 40 gallon tank, five kilowatt electric heater 
and a small 24 gallon heat bank. 
As will be seen the heat bank delivers the first six gallons with a rapid 
drop in temperature from 150.degree. to 105.degree. (at the left side of 
the chart of FIG. 5) when the circulator and boiler are called in; forced 
heat transfer than takes place and the water temperature quickly recovers 
to the 150.degree. range. The system was experimentally operated without a 
mixing valve which would be helpful in balancing the temperature supply 
but the graphic illustration of FIG. 5 shows the results utilizing the 
stored bank of heated water in heat bank 10 and alternatively, a separate 
electric heater. 
The FIG. 6 chart shows how a domestic hot water draw quickly reduces the 
bottom temperatures of the heat bank and produces the "on" signal for the 
burner and the circulator. In this case the surface thermostat 50 at the 
lower end of the heat bank 10 closes after one minute of draw of water 
initially at 150.degree. F. Within one minute, reduction of hot water 
output temperature to 105.degree. will operate sensor C to energize the 
furnace and boiler to supply continuous heated water to the heat bank 10 
until the level of output heated domestic water is restored. 
While there is here shown a boiler and a heat bank which is replenished by 
the boiler when the temperature at the lower end of the heat bank drops to 
a pre-determined level, the system lends itself to utilization in 
connection with a solar energy heat input which may be used primarily as a 
supplement. The input of heated water derived from solar energy into the 
heat bank 10 will, to the extent that it provides additional heated water 
for the heat bank 10, reduce the amount of energy required from the 
furnace and boiler and hence reduce the required firing cycles. 
Therefore, as shown in the dotted line addendum to FIG. 1, a solar heater 
collector 200 of any desired nature may be provided having a pipe of 
conduit 201 extending therefrom down to and into an area adjacent the 
bottom of heat bank 10 and another pipe or conduit 202 extending into but 
adjacent the top of heat bank 10. Thus, the conduit 201 will be connected 
to the lower temperature area of the heat bank 10 and the conduit 202 will 
be connected to the higher temperature area of the heat bank 10. A solar 
water circulator 204 may then be provided in the conduit 201. The water in 
the heat bank 10 together with the water in conduits 201 and 202 and the 
solar heater 200, will be a continuous closed system in parallel with the 
closed circulating hot water system including the pipe 23 from the boiler 
15 to the heat bank 10 and in parallel with the heating system. 
When the sensor 50 at the lower end of heat bank 10 calls for the infusion 
of heated water and the sensor 206 at the solar heater is in a position to 
provide such heated water, then the circulator 204 will be caused to 
operate until the heated water in heat bank 10 is replenished as 
determined by the sensor 50. If, however, during operation, the sensor 206 
should show a reduction in the temperature of the water in the solar 
heater 200, then the operation will be transferred from the circulator 204 
to the circulator 13 and at the same time a signal will be transmitted to 
the burner 20 to fire. Sensor 206 (see also FIG. 7) is a relay which, when 
there is a sufficient heat level in the solar heater, will prepare a 
curcuit for operation of the circulator 204 in response to sensor 50. If, 
however, there is insufficient heated water in the solar heater 200, then 
the sensor 206 will open the prepared circuit to the circulator 204 and 
will close the circuit to the circulator 13 and the burner 20. The 
circulator 13 and the burner 20 of boiler 15 will thereafter operate only 
when the sensor 50 at the lower end of the tank 10 indicates the need for 
input of additional heated water into the tank 10. Therefore, when the 
water that is in the solar heater is at a sufficient elevated temperature, 
the circulator 13 and the burner 20 are cut out of the circuit which is 
controlled by the sensor 50. When the water at the solar heater 200 is at 
a lower temperature, the sensor 206 is operated so that the circulator 204 
is cut out of the circuit, while the circulator 13 and burner 20 are 
connected to the sensor 50. 
In the foregoing, the present invention has been described in connection 
with preferred illustrative embodiments thereof. Since many variations and 
modifications of the present invention should now be obvious to those 
skilled in the art, it is preferred that the scope of this invention be 
defined, not by the specific disclosures herein contained, but only by the 
appended claims.