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[EnergyPlus_Support] Re: on/off boiler
Dear Dr.Li,
yea you are right i agree with you completly about " comfort requirement and energy saving does not go together that "
, but you know in my country IRAN , in almost building there is the system with two thermostat : one thermostat is for boiler and another for its pump , and usually pump starts earlier than boiler .
by the way for modeling this on/off boiler that works at its maximum capacity i used :
maximum part load ratio = 1
minum part load ratio =1
optimum part load ratio =1
is that right?
thanks
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, YuanLu Li <yli006@...> wrote:
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> You said: "A central heating system consists of all the pipe work and radiators that are connected to the boiler. The boiler provides the heat but, it's the pump (Circulator) that moves the heated water from the boiler through the pipe work to the radiators, and back to the boiler for re-heating. the system is controlled by two setpoint that one of them is on return water pipe from radiator and another is on outlet pipe from the boiler . the pump works till the return water temperature of radiator reachs 70°C. Then it stops until the water temperature get lower than 70°C once again.the boiler works at its full capacity till the outlet water temperature of boiler reachs 80°C. Then it stops until the water temperature get lower than 80°C once again. thanks "
> The above is a text book version. In practice there are many other ways. Combination boiler does not know whether the reduction in temperature is from the radiators or from the water main.===============================I have hands on experience on feeding a boiler in 1958 in London, England. The building has two boilers burning coke. One for hot water supply and one for the building radiation system. The boiler capacity was not constant, it depends on how often you stoke it, and how you set the chimney damper position. The circulation pump is on only for the first 15 minutes in the morning, when the boiler is restarted, because it went off during the night. After then the temperature difference between the up pipe and the down pipe is sufficient to keep the water circulating. There is no temperature sensors on the pipes. The room thermostat turns on and off the radiators. When the occupant complaint to the management that the radiators are cold, the circulation pump would be turned on again for a while, while the stoker build up the fire again. I admit this is an old system which you may not find it in EPlus simulation. There was no need to keep the water temperature at 80°C, so long it is higher than the highest room temperature you need. So long the upper floor PLR at the top floor is not one, all lower floor would get enough heat. I was a volunteer stoker for weekends. When my radiator does not cycle on and off, it is time to stoke the boiler, clear the ash and load up with more coke. This is why I kept saying comfort requirement and energy saving does not go together.ASHRAE guide lines are biased towards comfort.==========================What you have described is one particular type of boiler which use a burner which can be turned on and off, controlled with two thermostats. There is no problem simiulating that in EPlus. However, a real gas boiler (furnace and tank) may not use two thermostats as you described. This may also be the reason why only one value is given to set the zone thermostat. Your home thermostat also only allow you to set one value. The set back adjustment is not on the same lever. Only a temporature sensor thermostat (usually digital) require an on and off setting to control an on/off switch, because the thermostat do not have a built in default set back nor the switch. The default value must be another input value. In a GAS burner, there is a pilot lighter, inlet and chimney air flow safety interlock, etc. in the system. The thermostat initializes the check functions and then turns on the gas supply. Do you want to simulate all these as well. If you do, it can be donel, by using the available managaers. If one check point is not on, the system can be locked out and issue a warning.. =============================With an electrical heater, all the heat is in the zone. Therefore no additional simulation is required. ===========================If you are interested only in the annual operating cost, do you need to simulated down to this level. If the LEED does not need it, no body else would. ============================I do check all the safety operations for a gas furnace installed, and must know the operating sequence to certify that it is working properly. I know I am long winded. I think, it also help to answer the question why use simulation.Digital computer controlled system is very flexible, but not easy to design. Simulation helps to pin point the operational sequential problems. EPlus documentation assume that the user has some exposure to a real system. I see no reason why a new user should start with a one zone water VAV system, and then say the EPlus cannot complete the simulation, with thousands of set point not met warnings using annual weather file. Dr. Li
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> From: t.t111ir@...
> Date: Wed, 18 Jan 2012 14:48:28 +0000
> Subject: Re: [EnergyPlus_Support] on/off boiler
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> thanks Dr.Li for your answering,
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> Is that what happens when you turn on a tap in your bath room? The boiler comes on immediately. The fire stops when the tap is turned off. This is the way the inline heater works.
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> but it is not Combination boiler that it works by taking cold water straight forward the mains supply and heating as you need it. when you turn on a tap, water drawn from the mains , heated in the boiler and comes straight out of your tap piping hot.
> it is traditional boiler .
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> A central heating system consists of all the pipe work and radiators that are connected to the boiler. The boiler provides the heat but, it's the pump (Circulator) that moves the heated water from the boiler through the pipe work to the radiators, and back to the boiler for re-heating.
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> the system is controlled by two setpoint that one of them is on return water pipe from radiator and another is on outlet pipe from the boiler .
> the pump works till the return water temperature of radiator reachs 70°C. Then it stops until the water temperature get lower than 70°C once again.
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> the boiler works at its full capacity till the outlet water temperature of boiler reachs 80°C. Then it stops until the water temperature get lower than 80°C once again.
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> thanks
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> From: YuanLu Li <yli006@...>
> To: EnergyPlus_Support <energyplus_support@xxxxxxxxxxxxxxx>
> Sent: Wednesday, January 18, 2012 4:30 PM
> Subject: RE: [EnergyPlus_Support] on/off boiler
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> Is that what happens when you turn on a tap in your bath room? The boiler comes on immediately. The fire stops when the tap is turned off. This is the way the inline heater works.
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> A portable radiator heater has a thermostat switch to turn on and off the supply. There is no circulation pump.
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> What is missing in your simple (basic) assumption? If you have a small room, the boiler temperature may not change.
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> ====================
> A storage tank works the way you have described, between the charging cycles.
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> Dr. Li
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> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> From: t.t111ir@...
> Date: Wed, 18 Jan 2012 07:44:53 +0000
> Subject: [EnergyPlus_Support] on/off boiler
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> I am trying to model a very basic water heating system . The system consists of:
> 1) Boiler
> 2) Circulation pump
> 3) Radiators
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> in each time during which the boiler is turned on, the boiler operates at the full load, delivering the amount of energy equal to its design power.
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> In fact, what I want is to simulate the oscillations of the air temperature of the room because of the radiator i have. the boiler works at its full capacity till the outlet water temperature of boiler reachs 80°C. Then it stops until the water temperature get lower than 80°C once again.
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> i want to know could i model this ? and help me about it please.
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> thanks
>
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