I am modelling a hospital which has humidification within the AHUs. The required steam is produced using natural gas, which means I need an Exceptional Calculation because the software used allows only electric humidifiers.

I read in the forum that humidifcation is a process load and as such the consumption must be the same between the two buildings. Can I add the energy consumption later on after the simulation in the calculator? Or should I also calculate the humidifcation for the baseline building the same way I will for the proposed building? If I did it this way, I think the results for the two buildings would be different (different air flows) and therefore not energy neutral, as required for process loads.

Thank you all.

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Marcus Sheffer

LEED Fellow

7group / Energy Opportunities

LEEDuser Expert

4454 thumbs up

Tue, 11/10/2020 - 15:51

In this case the energy use can be different, it is the system you model that must be identical. This is not a simple, stand-alone load so you must simulate it within the software or make the case that your calculations account for all the interactive effects of this system. One of the unwritten rules of energy modeling is to always use software that can simulate the systems being modeled, especially if there are interactive effects or to have a peer reviewed work around to be able to cite if the software can't directly model a system. So you are going to have to demonstrate the thermodynamical validity of your calculations, especially if you end up showing savings.

David Eldridge

Energy Efficiency Ninja

Grumman/Butkus Associates

LEEDuser Premium Member

64 thumbs up

Tue, 11/10/2020 - 23:01

Depending on the software you may be able to use the built-in model with some assumptions applied to model the fuel use instead of making an exceptional calculation. A workaround inside the software may be easier to review and verify interactions than supplying separate spreadsheets. Especially for a hospital that could have significant amounts of humidification energy. "Especially-especially" if one of your energy efficiency measures would affect the airflow volume between the proposed and baseline cases, it would NOT be expected to have identical humidication energy use if the quantities of outside airflow, return airflow, and supply airflow are different between the cases resulting in different quantities of moisture to be added to provide the same temperature and humidity requirements. The generation efficiency of the humidifiers may be the same, but not the total quantity of energy use. What software?

Davide Liviero

LEEDuser Basic Member

1 thumbs up

Wed, 11/11/2020 - 07:16

Thank you both. @Marcus: Given your response, I add a further question. You said that the system must be identical and I suppose you refer to the AHUs. Therefore, I would like to ask if I should use the same setpoints and reset rules I used in the proposed design also in the baseline building. I have already added a preheat coil with the same settings, as required by ASHRAE 90.1-2007. However, I am not sure also the other coils should be modelled identically. @David: I am using Design Builder v4.7. Unfortunately, the humidifier in this software is only electric. Therefore, I was planning to set as nominal electric power input of the items the power needed for humification (sensible + latent heat). Afterwards, I would have taken the sub-hourly energy consumption data and using a curve (efficiency vs part load ratio) I would find the natural gas consumption. This way, I use the built-in model and I do not make assumptions on the interactions.

Marcus Sheffer

LEED Fellow

7group / Energy Opportunities

LEEDuser Expert

4454 thumbs up

Thu, 11/12/2020 - 00:44

The humidification system and settings must be idential, not the AHUs.

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