Philadelphia Reflections

The musings of a physician who has served the community for over six decades

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Supra Complex Heating Systems

At the beginning of 1979, the price of domestic heating oil began to soar. Because natural gas was controlled by the Federal Government, this price remained fixed. It was evident that anyone who could switch from oil heat to gas heat would benefit greatly by doing so.

My home is a large Victorian house with 11 rooms that was built about 90 years ago. The House is not particularly well insulated, although it is very well built. The heating system was an old coal boiler that had been converted to oil. The oil burner itself was only 3 to 4 years old. The cost of converting to gas was approximately $2,300 and the saving that would result from the use of the less expensive gas was such that the payback period would be 3 years. It made economic sense to me to invest in this capital expenditure when the payback period was such a relatively short one.

To begin with, I would like to analyze the existing oil burner system. Feed water enters the system by means of an automatic valve that is set at a specific pressure. Water enters the system until that pressure was obtained and would then shut off. If the water exceeded a certain higher pressure, a relief valve opened allowing the water to escape from the system. An aquastat controlled the boiler water temperature and a circulating pump moved the water to the radiator when the thermostat called for heat.

The domestic hot water was also heated by this oil fired coal boiler. This was done by means of a summer/winter hook up consisting of copper immersed in the boiler water and an 80 gallon insulated storage tank that would collect the heated water.

When I first considered installing a new gas-fired boiler, the plumber suggested that I take out the old system and replace it with a new one. However, I saw no reason to do this as it was in good working condition. I decided that I would design a new system to work in parallel with or instead of the first system.

There was plenty of room in the basement and, since a hot water system lends itself to the type of arrangement P had in mind, it was relatively easy and practical to design a tandem system that could be operated in conjunction with or instead of the original one. The new system is basically very similar to the old one except it is fired by gas instead of oil. However, there are some significant differences. One is in the domestic hot water is heated. This is done by means of an instantaneous hot water coil. No storage tank is necessary because the rate at which hot water is used is less than the rate at which it can be heated. You can use hot water all day and all night and still have a sufficient supply. That theory is based on just one use at a time. In my house, two people cannot take showers at the same time in two different bathrooms because one would not have enough water pressure.

Because of the nature of the domestic hot water heating system in the gas furnace, it was decided to use the hot water storage tank from the oil burner system as a tempering tank for the new furnace. Cold water would come in from the main at approximately 45.F and would stay in the tempering tank in the basement and warm up to the ambient air temperature. The end insulation was removed to facilitate this. The water would then feed into the gas burner for heating up to approximately 120.F

After I had made my design, I reviewed it with the plumber and he suggested some practical inputs that I as an engineer hadn't considered. For instance, in using an instantaneous hot water system, a restrictor has to be put in the line so that the flow of hot water through the coil is not so rapid that the water flows through faster than the furnace can heat the water.

With the two systems that can be used together or separately, I have actually created a supra-system that can be operated in different ways. The normal way and the way that it is operated most of the time (now that natural gas is a good deal cheaper than oil) is as a gas burner with the burner domestic hot water storage tank acting as the tempering tank. A second way is to operate as an oil burner, just as previously, with the domestic hot water heated by the oil burner and stored in the storage tank. Both Systems can be operated together and this is done occasionally for very practical reasons. If I go on a trip in the winter and lower the temperature to 50.F and, upon returning, wish to increase the temperature in the house as rapidly as possible, I will put both systems on and can bring the house up to a comfortable temperature in about 1-1/2 to 2 hours. With just one furnace, it would take close to 4 hours. A third method that can be used, although I think it is an impractical one, is that you could use one burner to heat the house and the other one to heat the domestic hot water.

There are also two other combination's. You could use the oil burner to heat the house and use both the gas burner and the oil burner to heat the house and use both the gas burner and the oil burner to heat the hot water. You could also use the gas burner to heat the house and use both oil and gas burner to heat the water. This is really not a practical hook up and the only time it would conceivably be used as if one of my daughters was having a big house party where there would be a lot of showers, baths and shampoos and the girls wanted a guaranteed unlimited supply of hot water for the occasion.

One mistake that I believe was made in assembling the new system was that a separate feed water valve connected to the new furnace. I believe this occurred because the new furnace came equipped with the feed valves and, instead of just trying it into the existing feed water valves, the plumber automatically used the valves that were supplied. The system works satisfactorily the valves that were supplied. The system works satisfactorily this way but this unnecessary complexity did cause trouble once last winter. One of the radiators on the third floor cracked during a severe cold spell. I noticed the water leaking from the radiator on the third floor and the first thing I did was to turn off the feed water system. I had forgotten, however, that there were two feed water systems going into the Supra-system and, initially, couldn't understand why the water kept flowing from the cracked radiator. This is an example of the system becoming too complex so that, in reality, it becomes very cumbersome to control. Since I was the one who designed the system and was intimately familiar with it, I should have been fully aware of the fact that there were two feed water valves going into the supra-system. However, with the excitement of the cracked radiator and the dripping water, I had forgotten about this until I investigated thoroughly why the water had not stopped flowing.

Two other slight problems occurred that could not have been anticipated. One was that with the use of the modern designed high capacity circulating pump, a resonant type hum occurs when the system is calling for heat. This doesn't seem to be very noticeable in any room except the master bedroom and it became easier to get used to the hum rather than replace this circulating pump with a lower capacity one. The Second problem that developed was that as soon as the temperature in the boiler dropped below a certain point, the circulatory would shut off to allow the water temperature in the boiler to water from getting too cool, thereby cooling off the instantaneous hot water coil. This intermittent use of the circulator pump caused one particular radiator on the first floor no to get very warm because the circulator itself was only operating for a short period of time the hot water seemed to have trouble in getting to this particular radiator.

A complex as my new heating system seems to be, I believe it is a practical system for several reasons. First, it cost less to put the new system in tandem with the existing system than it would have to tear out the old and replace it with the new system. Second, by having two systems I have great flexibility as far as what kind of fuel to use. If the price of natural gas goes higher than oil, in less than one minute I can switch from gas to oil. Third, if one of the units develops a problem, the other unit can be brought on the line very rapidly and the house will stay warm. Fourth, the house can be brought up to temperature in approximately one-half the normal time because of the double heating capacity that is now in existence. Fifth, great flexibility was obtained with the domestic hot water system.

If the price of natural gas approaches oil while coal stayed low so that the installation of a coal furnace would have a payback period of 3 years or less, I would not hesitate in adding a third furnace. This might seem completely idiotic but, if it will pay for itself within 3 years, it would make economic sense. Since I have the room in the basement to keep adding furnaces, why not? of course one of the disadvantages of creating a supra-system that has approximately four times the complexity of a simple system is the difficulty in controlling it. Witness the problem that I had during the emergency of the cracked radiator! When I eventually sell my house, the new owner might be completely baffled by this complex system. Of course, all the valves and switches are labeled but, even so, it can be difficult understanding which valve to turn at which time. If the owner is completely ignorant when it comes to mechanical and electrical devices, he could solve the problem by just setting the system once and, when he feels he wants to change he could call the plumber.

One of the requirements, when a homeowner switches to gas heat in New Jersey, is that the house has storm windows. Another is that the system be controlled by a clock type thermostat works very nicely on a small house or on a house that has over 20 large cast iron radiators does not work properly from a practical aspect. What happens is that, if you lower the thermostat 5 to 10 degrees for night operations, when the thermostat calls for the day temperature the next morning, the furnace comes on and has to work very hard to heat enough water to raise the temperature of the whole system. By the time the house does come up to the day temperature, the cast iron radiator is so hot that, even though the furnace shut off, the temperature continues to rise about five degrees. The reason is that the cast iron radiators hold the heat and, even though the furnace has turned off, the house temperature goes up making it very uncomfortable and also defeating the purpose of the day/night thermostatic setting.

I had suspected that this would be the case, although I was not sure. The practical solution to this problem was that after the Public Service of New Jersey inspector made his rounds and saw that I compiled it every way, I then took out the clock thermostat and sent it back to the dealer and exchanged it for a regular single setting thermostat.

Since both heating systems can be used together and since each one has various sensing controls, one of the statements made by J.G. Miller in his book, The Need for a General Theory of Living Systems, would also apply to this heating system. Specifically, he said, "if there are multiple parallel deciders without a hierarchy that has subordinate and supra-ordinate deciders, there is not one system but multiple systems". In a sense, this is what I would have if I used the oil burner to heat the domestic hot water but then fed this domestic hot water into the gas burner instantaneous hot water coil to further heat it. Miller also talks about joint subsystems and he defines that as, "the case when a system is dependent for the process on a component it shares with another system". In my heating system, this would be the case with the 80-gallon storage tank. In one used as a storage tank for domestic hot water and yet, in another method of operation, it is used as a tempering tank for the instantaneous hot water coil in the gas unit. This same tank can also be used as part of a preheating system in conjunction with the instantaneous hot water coil.

Miller also talks about passive adaptation and, as an example, he talks about a heater controlled by a thermostat. Since I have two heaters controlled by two different thermostats, this is a very good example of passive adaptation and it can be used in such a way that if, for some reason or other unit to heat the domestic hot water, this could be achieved by setting the thermostat for the home heating at the desired temperature while the thermostat for the heater that was to heat the domestic hot water would be placed at a lower temperature to ensure that particular heater circulation would not come on to heat the house.

Another advantage of my supra-system is it provides a back up in the event that the house is empty and the primary heater fails to function. This can be achieved with my dual system by setting one thermostat at, let's say, 50.F and the other thermostat at 45.F. The way this would work is that normally the house would be heated, for instance, by the gas furnace and the temperature in the house would remain at 50.F. However, if something happened to the gas furnace and the unit did not come on, the oil furnace would automatically come on when the temperature dropped to 45.F, thereby providing insurance against many cracked pipes and radiators.

The way my two heating systems are interconnected, they can be operated either as an integrated system or as a segregated system, depending on the requirements at the time. According to Miller, " the more integrated a system is, the more one part is likely to influence or control another". Generally speaking, however, my system is operated as a segregated one except for unusual circumstances. The two systems are very compatible and, if both are working at the same time, they work together without any conflict.

Miller maintains, "The general direction of evolution is towards greater complexity". He made this statement in relation to living systems but I believe this statement is also true in mechanical systems. As we evolve our various mechanized units, whether they be automobiles, airplanes or heating systems, the direction is towards increased complexity rather than greater simplicity.

Originally published: Monday, April 05, 2010; most-recently modified: Friday, May 31, 2019

what about an potbelly stove
Posted by: [none]   |   Feb 5, 2011 8:36 AM