Units 😈

[praftery]

Switching the toggle does not actually change units on the loads tab or load selection table popup. Same for Equip and Emissions tabs.

[t-kramer]

Unit toggle now implemented for most parts of the app, except:

• Load selection table pop up
• Data download

Will work on that next.

[t-kramer]

@praftery @urwahah To manage all unit conversions, I'd like to create a clear unit registry that shows the SI units we are using across the app and their counterparts in IP. I noticed that we probably have to separate between units we use for calculations/exports (mostly base SI + corresponding IP units for dataframe download) and those shown in the UI and charts (which often differ from the base units used in calculations).

Could you guys help me with that? IP units are still confusing to me (especially power/energy, etc.), so I'd like to hear your opinion on what to use in which case (basically: What is the industry standard?). We could start with a simple Excel file (e.g. based on exported results dataframe) and I'll convert it into something for Python like later. I can get started and send it around for you guys to fill in the gaps 😜

[praftery]

Sure. ASHRAE has a comprehensive SI guide which maps units to/from I-P here: https://www.ashrae.org/technical-resources/ashrae-handbook/the-si-guide The main issue for the tool is that it's not a one to one mapping. SI only has one unit for any given quantity (m, s, J, W). While there are exceptions that are in not officially SI but are in common use (kWh), it is very rare. In contrast, I-P has lots of units for the same quantity, and it's particularly bad for energy. The most common for HVAc are probably BTU, therm, ton (TR, of refrigeration), ton (THR, of heat rejection), but there's also boiler hp, lbs of steam, ft-lbf, quad... the list goes on and on. Worse, many of those are also used interchangeably as units of power with underlying (and unstated) assumptions that the unit of time used is an hour. So we'll need to decide how to handle that. Options: 1) We could just use only one conversion (e.g. BTU for energy, BTu/hr for power, with kBTU and kBUT/hr used for larger values) and leave it at that. That would be far simpler, and far less error prone. I think this is probably the best approach for the output data csv file format, just for simplicity. The downside is that if we do that for displaying results, thye will appear in a way that users are not familiar with (the main ones are probably that chiller capacity will be shown in BTU/hr not tons (similar for cooling towers), and gas use will not be in therms). 2) We define a specific mapping for all the different sections of the tool. i'm leaning towards 1. Thoughts?

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On Thu, 5 Mar 2026 at 16:30, Toby Kramer ***@***.***> wrote: *t-kramer* left a comment (CenterForTheBuiltEnvironment/decarb-tool#78) <#78 (comment)> @praftery <https://github.com/praftery> @urwahah <https://github.com/urwahah> To manage all unit conversions, I'd like to create a clear unit registry that shows the SI units we are using across the app and their counterparts in IP. I noticed that we probably have to separate between units we use for calculations/exports (mostly base SI + corresponding IP units for dataframe download) and those shown in the UI and charts (which often differ from the base units used in calculations). Could you guys help me with that? IP units are still confusing to me (especially power/energy, etc.), so I'd like to hear your opinion on what to use in which case (basically: What is the industry standard?). We could start with a simple Excel file (e.g. based on exported results dataframe) and I'll convert it into something for Python like later. I can get started and send it around for you guys to fill in the gaps 😜 — Reply to this email directly, view it on GitHub <#78 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ABXJHKXGKCYSFLJRQNG65E34PIL27AVCNFSM6AAAAACV22BWSOVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHM2DAMBYGY4DKOJQGI> . You are receiving this because you were mentioned.Message ID: ***@***.***>

-- Regards, Paul

[urwahah]

agreed that we should standardise energy units to BTUs, especially for plots. it's definitely a little nonintuitive to not see tons for cooling but also not a difficult conversion to do manually / similar for therms

[praftery]

Sounds good to me. So its: Temperature: Celsius -> Fahrenheit (becareful to adjust the calculation for any temperature difference conversions - I don't think we currently have any in the tool, but just in case!) Energy: Wh -> BTU Power: W -> BTU/hr distance: m -> ft mass: g -> lb A few other points: 1) For powers I'd use utf-8 symbols (e.g.²) instead of font superscripts. 2) There are compound units too. Looking through the only one we have currently is gCO2e/kWh. We should convert to lbCO2e/kWh . 3) There are use cases where it would be handy to normalize by building floor area. Or a user might want to toggle back and forth. e.g. W vs W/m² 4) On prefixes. For both SI and IP cases I'd store the data as the base unit without a prefix. We can add prefixes where needed when displaying values to the user, to keep it to a max of 3 digits before the decimal point. We mostly already do this but not everywhere (e.g. I think we store kg, not g) so there is some work to change this. However, it's probably less error prone. Doing it consistently would for example resolve the issue on the results plots where there's often a prefix in the axis title and then another prefix on the axis tick marks (see below: kWh, then 10 k, should be 10 MWh). 5) Last, just a heads up that there are some I-P units with weird prefix edge cases. For example, MBTU and kBTU both mean 1000 BTU, and sometimes prefixes are doubled up like MMBTU = 1000000 BTU. We should only use the character to multiplier map for SI prefixes, for all prefixes. For example, k=1000, M=1000000, etc.. So we only represent 1000 BTU as 1 kBTU, we never use MMBTU, etc. [image: image.png]

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On Fri, 6 Mar 2026 at 10:20, urwa irfan ***@***.***> wrote: *urwahah* left a comment (CenterForTheBuiltEnvironment/decarb-tool#78) <#78 (comment)> agreed that we should standardise energy units to BTUs, especially for plots. it's definitely a little nonintuitive to not see tons for cooling but also not a difficult conversion to do manually / similar for therms — Reply to this email directly, view it on GitHub <#78 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ABXJHKTAFNIYG4CTJXDOS3L4PMJHNAVCNFSM6AAAAACV22BWSOVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHM2DAMJTGI3TOOBSG4> . You are receiving this because you were mentioned.Message ID: ***@***.***>

-- Regards, Paul

[t-kramer]

Hi @praftery @urwahah,

I’ve created an overview with all variables and their current units in the tool. Please review and comment. I used Google Sheets for easy tracking.

Some variables are implemented, while others need it. Most open ones refer to unit conversion for the building load selection table and dataframe download. I’ll adjust them once we agree on a convention.

I prefer standardizing by entity, like Paul suggested, using a default for energy, power, mass, temperature, etc. and store all conversion information locally and feed it to wrapper. A simplified mapping could look like this (I’d add conversion factors too):

# base: for calculation only, SI and IP for app display and results export

unit_map = {
    "energy":            { "base": Wh,          "SI": kWh,        "IP": BTU },
    "power":             { "base": W,           "SI": kW,         "IP": tons },
    "capacity":          { "base": W,           "SI": kW,         "IP": tons },
    "temperature":       { "base": °C,          "SI": °C,         "IP": °F },
    "emissions":         { "base": kg CO₂e,     "SI": kg CO₂e,    "IP": lb CO₂e },
    "area":              { "base": m²,          "SI": m²,         "IP": ft² },
    "load_intensity"     { "base": W/m²,        "SI": kW/m²,      "IP": BTU/h/ft² },
    "energy_intensity"   { "base": Wh/m²,       "SI": kWh/m²,     "IP": BTU/ft² },
    "ng_leakage_rate":   { "base": g/kWh,       "SI": g/kWh,      "IP": lb/kBTU },
    "emissions_rate":    { "base": g CO₂e/kWh,  "SI": g CO₂e/kWh, "IP": lb CO₂e/MBTU },
    "mass":              { "base": kg,          "SI": kg,         "IP": lb },
    "gwp":               { "base": kg CO₂e/kg   "SI": kg CO₂e/kg, "IP": lb CO₂e/lb }
}

Please let me know if you think we need more detail when breaking things down into categories. I understand that there are edge cases we might need to accommodate. 🤙🏼

[t-kramer]

Renaming this issue for ongoing discussions/issues around units.