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How to model a steam district heating loop? [closed]

asked 2016-04-07 08:03:32 -0500

FSilenzi's avatar

updated 2016-04-07 08:04:10 -0500

I have the need to model a loop in openstudio that will provide the heat to my VAV hot water loop, the domestic hot water and the a baseboard radiator, via a U pipe heat exchanger. I have read here that there is no heat exchanger in E+ that can be operated with steam (causing errors in OpenStudio simulations), and I need to use a hot water boiler. Has this feature been included in any of the latest releases of E+?

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Closed for the following reason not a real question by FSilenzi
close date 2016-04-11 06:41:35.742842


You're not modeling the district heating itself are you? You're just buying steam from the utility?

Julien Marrec's avatar Julien Marrec  ( 2016-04-07 08:15:02 -0500 )edit

Yes I want only the district heating to provide steam at 180°C and 24 bar. I am not interested in how the steam itself is produced, since the building is receiving heat from a internal steam loop and uses the resulting hot water for the use I indicated above.

FSilenzi's avatar FSilenzi  ( 2016-04-07 08:53:46 -0500 )edit

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answered 2016-04-07 09:20:20 -0500

updated 2016-04-07 09:46:53 -0500

I wouldn't care if I were you, and there's a good reason for this: the DistrictHeating object is a hot water element anyways.

To be a little more helpful, here's what I would do. I would model the system AFTER the main heat exchanger, which is where is the property line is in many cases:the utility is responsible for the heat exchanger, since a failure can affect their global distribution system, and the property is responsible for whatever is after.

You can calculate the "Nominal Capacity" (W) of the heat exchanger and use that in the DistrictHeating (or let it autosized).

In the end you'll get a DistrictHeating Energy in Joules, which you can always convert back to pounds of steam at 180°C/24 bar if that's what you need.


Don't model the heat exchanger at all. Just model the building loop with the district heating object on the supply side, and your VAV terminals on the demand side. Use a setpointmanager that will match your proposed building loop operation: for example it could be an outdoor air reset and the steam flow is throttled to maintain 80°C water outlet temperature when it's really cold outside, and 60°C water when it's mild outside.

If you need to have separate loops (2 heatings loops for 2 different part of the building, and 1 DHW loop for example) you can always do two things:

  • Model 3 different loops, each served by a different district heating object (in the end, all it's cares about is energy delivered). This is the easiest.
  • Or you can model one master plant loop with the district heating object on the supply side, and 3 HX on the demand side. Control this loop to have a constant temperature. I'm actually wondering if you couldn't set that loop to be at 180°C or if EnergyPlus will be unhappy about it even if you set the PlantLoop maximum temperature to 200C (if you try it, let me know). After all, water in liquid form can be heated to 374°C (provided you can pressurize it at ton)
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My doubt is a slight different, if I use a district heating object it will be delivering water, but I cannot define any quantity related to it. I mean, I can only define the district heating size but not the temperature or the pressure of the energy carrier fluid. Can't this lead to a heat exchanger sizing error? If I exchange at lower T the apparatus should be bigger or with a higher efficiency.

FSilenzi's avatar FSilenzi  ( 2016-04-07 09:31:26 -0500 )edit

I edited my answer

Julien Marrec's avatar Julien Marrec  ( 2016-04-07 09:47:07 -0500 )edit

I have already tryed to set HX maximum temp to 200 °C and then using the setpoint manager to fix the temperature to 180°C, after setting the plant loop fluid type to steam and the max T to 200 °C. The error I had was related to the plant overheating "GetDensityGlycol: Temperature out of range (too high) for fluid [WATER] density " so I started to wonder if this could introduce severe errors into the simulation and thought about opening this new question. Anyway I think I will follow your advice and simply link the DHW source to the hot water loop, it seems the most convenient solution.

FSilenzi's avatar FSilenzi  ( 2016-04-07 10:09:13 -0500 )edit

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Asked: 2016-04-07 08:03:32 -0500

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Last updated: Apr 07 '16