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Understanding BEopt DView outputs

lance_p | Posted in Energy Efficiency and Durability on

OK, so for some of you this is going to seem like a “duh” question. I’m using BEopt to model the energy use of our new home and I’m more than a little confused as to which toggles I should be using in the DView output.

For example, if I want to see the BTU output of my heating equipment, in this case a GSHP, what toggle do I use to show the actual BTU output over time? This is imortant for equipment sizing, but there are SO many options:

Source Energy
-Total (*) (Btu)
-Total (E) (Btu)
-Heating (E) (Btu)

Site Energy
-Total (E) (kWh)
-Heating (E) (kWh)

Delivered Energy
-Heating Delivered (main) Btu)

Is there a page or document I can be pointed to that gives a thorough description of what all of these different DView options actually mean? I’m trying to determine my peak heating (and cooling) loads for equipment sizing, but I get numbers all over the map depending which options I look at.

Thanks!

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Lance,
    It's been a while since I've used BEopt, so I'll let someone else direct you to the best tab. But you may have a few misconceptions about energy use.

    You wrote, "What toggle do I use to show the actual BTU output over time? This is important for equipment sizing."

    In fact, when it comes to equipment sizing, you don't care about energy use "over time." You only care about energy use per hour on the coldest night of the year. Monthly or annual energy use is irrelevant. For more information on equipment sizing, see these articles:

    How to Perform a Heat-Loss Calculation — Part 1

    How to Perform a Heat-Loss Calculation — Part 2

    For equipment sizing, you are interested in site energy, not source energy. For more information on site energy vs. source energy, see this article:

    Understanding Energy Units

  2. Expert Member
    Michael Maines | | #2

    Lance, while the DView (also called Hourly Output) graphs are informative, for sizing HVAC equipment there is an easier way. On the Output page, there is a graph at the bottom left with a drop-down menu. Choose "Graph Type-->HVAC Capacities (kBtu/hr)." It's also a good idea to look at "Graph Type-->Loads Not Met (Hrs/yr)" which will correspond with spikes on the DView graph, but as long as it's only a few hours a year it's not a big deal.

    I have not modeled a ground source heat pump but I don't see why it wouldn't work the same as any other equipment choice.

  3. lance_p | | #3

    Martin, thanks for the links.

    I'm sure I've read the heat loss calculation pages before, but I will review anyway. Once I have my BEopt modelling nailed down with the latest version (2.8) I plan to do some rough manual calculations just to make sure the software outputs are in the ballpark (i.e. to make sure I didn't mess something up bigtime).

    By "over-time" I was implying Btu/Hr, I just didn't say it that way. "Rate" is the word I was looking for, I guess. Site energy makes sense, but DView only provides it in kWh which requires calculating Btu/Hr for equipment sizing. It didn't make much sense, hence my questions.

    Michael, thanks for the tip!

    I remember reading that BEopt would suggest equipment requirements but I didn't know how to get there. I'll check it out tonight.

    I plan to model the house with several different heat sources just to make sure the heat loss estimations are consistent between them. I've read that BEopt has had teething problems with different equipment types in the past and want to rule that out as a possible issue.

  4. EthanT | | #4

    Martin and Michael... Working closely with my Mechanical engineer to figure out if the Minotair+5000W heater is a reasonable replacement for Minotair+Hydronic (heated via HPWH) has led me to dive into the complexities of the BEOpt DView graphs to figure out which portions of the year the backup resistance might be running. The same would be useful for someone with an undersized minisplit and backup baseboard electric. Added to the complexity is the possibility of burning wood instead of turning on the baseboards... so the most important thing to do is pretend that the resident is too tired or unable to haul wood, while adding the wood stove into the back-of-napkin portion of the calculations.

    From this, I get something pretty rough that tells me that given the Minotair rated capacity at 17 degrees outdoor of 5600 BTU/hr that my 5000w supplemental heater would run for some portion of something in the range of 20 days throughout the year.

    One more request to BEOpt would be an ability to separate out Heat pump delivered heat and supplemental resistance electric heat... or maybe it's buried in there somewhere...

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