Re: [EnergyPlus_Support] Load Calcultations

I wish I could think as clearly and bring it so concisely to paper. Great answer. I'm going to rample my less concise thoughts a further step. The use of the componant loads report was to get an idea where the "weak spots" were, so that you could think about "strengthening those componants. Perhaps some were too good, and you could apply those construction costs better elsewhere.

So how can you do the same analysis in e+? There exists a new report called Sensible Heat Gain and Sensible Heat Gain at Peak Heating (or similar...I'm not sure of the exact name). So basically you can see in this report where energy flows in and out of a zone. Not by componant, but by type, e.g. Infiltration gain, infiltration loss, hvac air gain/loss, active radiative surface gain/loss, solar gain/loss...basically the whole zone energy balance including through zone total componants. It's not the same, but it is a good start to understanding the energy flows in relation of magnitudes (more wall insulation is not helping much when you have an 80% WWR, just decrease the WWR by 5% for double the effect of increased insulation).

As Joe suggested, the zone loads calcs with purchased air is also a good tool. If you have the zone loads and the rated U-Values and areas of the zone's componants, you could back calculate the componant loads at the rated U-value rated conditions as they include the airfilm resistance based on appropriate convection coefficients, right?

It's too early to think this hard!

Jean

On 11.12.2013, at 22:12, Joe Huang <YJHuang@xxxxxxxxxxxxxxxxxxxxxxxx> wrote:

Seeing as how there haven't been any responses to Rodrigo's question, I'll take a shot at it, but bear in mind that I haven't pondered this aspect of EnergyPlus for over ten years and might be outdated in my perceptions. If anyone has a better answer, please correct me.

There's not a quick answer, because DOE-2 (the engine behind eQUEST) and EnergyPlus work differently, so that you can't always get the same reports. For the benefit of those unfamiliar with DOE-2, the LS-B report gives the component loads breakdown (wall, roof, lights, etc.) for the days with the largest heating and cooling loads. These are actually the heat flows to the spaces calculated by DOE-2's LOADS module at fixed reference temperatures, and are approximate since the true indoor temperatures are not solved until the following SYSTEMS module.

EnergyPlus, however, does not distinguish between LOADS and SYSTEMS, but simulates both within each time step. Thus, if you ran EnergyPlus with just the building model, you will not get the reference loads (in the DOE-2 sense), but the floating building conditions with neither heating nor cooling. If you want to get something similar to the LS-B report, you will have to add a fictitious system (used to be called PurchasedAir) and then set the heating and cooling setpoints to the same reference temperature as you would have used in DOE-2 (preferably the annual average indoor temperature). You can then find the days with the largest heating and cooling loads. But if you have to go through all this effort, why not simply use the actual thermostat schedules, which should give you more accurate peak loads, particularly for commercial buildings with intermittent operations? Lastly, don't expect to get the component loads as in the LS-B report, because EnergyPlus doesn't work that way (for those who like to quibble, yes you can get the component heat flows, but that's not the same as the loads).

Joe
Joe Huang
White Box Technologies, Inc.
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On 12/10/2013 1:01 PM, Rodrigo Cerqueira wrote:

Hi,

Iâ??m new in Energy Plus and I want start to use it to load calculations. I used to do that in eQuest. Can I have a report like LS-B (DOE2)? Normally in eQuest, I make just the shell model, with the zone internal loads and I run the simulation to get the peak heating and cooling loads. Can I do the same with Energy Plus? if so, which variable should I select to get the results?

Thankâ??s

Rodrigo

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