I'm currently working on producing an energy model for a building provided with biomass-fuelled CCHP generation.
The building itself is a 24 hour operating, high cooling load building. Therefore the CCHP will provide a base-load of cooling through absorption chillers and electricity generation as well as domestic hot water.
However CCHP in IES only seems to operate when there is a heating load assigned to it and this is not how the system is designed to operate.
As there is only a heating load for a small fraction of the running hours of the building, the CCHP plant will not generate cooling or electricity for the majority of the time.
Has anyone experienced a similar problem before? Perhaps a workaround is necessary?
CCHP for a net cooling load building
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andrewmackay
- VE Newbie
- Posts: 8
- Joined: Tue Nov 10, 2009 12:37 pm
Re: CCHP for a net cooling load building
obviously this will be dead now... but...
What arwe you doing this in? ApacheSim or PartL?
What arwe you doing this in? ApacheSim or PartL?
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andrewmackay
- VE Newbie
- Posts: 8
- Joined: Tue Nov 10, 2009 12:37 pm
Re: CCHP for a net cooling load building
It was in Part L but I think the same problem occurred in Apache too.
I gave up on this one in the end. I could get the CCHP to work when there was no heating load by setting the "minimum output fraction of rated heat output" to 0.
Although obviously this isn't realistic as there will be a minimum output of the CCHP plant.
I gave up on this one in the end. I could get the CCHP to work when there was no heating load by setting the "minimum output fraction of rated heat output" to 0.
Although obviously this isn't realistic as there will be a minimum output of the CCHP plant.
Re: CCHP for a net cooling load building
Andrew,
IES isn't a very good system simulation tool. It's more of a jack of all trades, so when it comes to creative / specialised / non-cookie-cutter system design, it doesn't have the flexibility to allow for these systems to be analysed. We've run into the same problem with CHPs, geothermal, heat recovery, etc, time and time again, and the basic workaround we have (system-wise) is to have IES calculate the plant loads, output to Excel, and create the system dynamics there in Excel (or MATLAB, or TRNSYS, or whatever tool you choose really) and do our plant design there. Doing this requires that you figure out exactly what's included in the different Apache outputs, which isn't exactly straightforward but it's do-able.
When you think about it, say you have a really complex building, with MacroFlo, with Suncast, with Radiance, and all your loads are calculated and it took 24 hours to run the simulation... do you really need to re-run the whole thing to see the effect of changing plant properties? Not necessarily. However IES does not offer the possibility to rerun a new system on a pre-existing results file. Therefore the solution (for us) has been to do most system simulation externally from IES. It's more work, and the Excel spreadsheets can get really massive, but we have greater control over what we can simulate. Also, until IES provide the tools for complex system design -- preferably script-based -- I don't see this changing anytime soon.
[just a bit of editorialising, I'm not saying this in response to you specifically but it's just a general comment on building simulation]
I think it's important, as engineers, never to lose sight that we are primarily engineers, not software operators. IES is just a tool, and never lose sight of what it can or can't do. Everything that IES does you should be able to do it yourself -- though probably much more slowly. Don't let the technical limitations of IES prevent you from designing the best system for your building.
IES isn't a very good system simulation tool. It's more of a jack of all trades, so when it comes to creative / specialised / non-cookie-cutter system design, it doesn't have the flexibility to allow for these systems to be analysed. We've run into the same problem with CHPs, geothermal, heat recovery, etc, time and time again, and the basic workaround we have (system-wise) is to have IES calculate the plant loads, output to Excel, and create the system dynamics there in Excel (or MATLAB, or TRNSYS, or whatever tool you choose really) and do our plant design there. Doing this requires that you figure out exactly what's included in the different Apache outputs, which isn't exactly straightforward but it's do-able.
When you think about it, say you have a really complex building, with MacroFlo, with Suncast, with Radiance, and all your loads are calculated and it took 24 hours to run the simulation... do you really need to re-run the whole thing to see the effect of changing plant properties? Not necessarily. However IES does not offer the possibility to rerun a new system on a pre-existing results file. Therefore the solution (for us) has been to do most system simulation externally from IES. It's more work, and the Excel spreadsheets can get really massive, but we have greater control over what we can simulate. Also, until IES provide the tools for complex system design -- preferably script-based -- I don't see this changing anytime soon.
[just a bit of editorialising, I'm not saying this in response to you specifically but it's just a general comment on building simulation]
I think it's important, as engineers, never to lose sight that we are primarily engineers, not software operators. IES is just a tool, and never lose sight of what it can or can't do. Everything that IES does you should be able to do it yourself -- though probably much more slowly. Don't let the technical limitations of IES prevent you from designing the best system for your building.