House in Balance technical note
How the model works, what to trust most, and where it stays deliberately approximate.
This page explains the logic behind the public guide for a critical practitioner. It separates official references, literature-informed logic and model-specific calibration so the tool does not pretend to be more exact than it is.
Use this as a route map first. Each section answers one expert question without turning into a generic whitepaper.
The public guide uses a deliberately compact concept-stage energy model for sensitivity reading. It is not a formal compliance engine. In the main preset row, the benchmark stays fixed: the same 140 m² house, the same north Lake Como climate, the same two-storey massing, the same compactness and the same solar-access base. The central question is simple: if that benchmark house stays fixed, how do construction standard, glazing logic, ventilation, shading and systems shift winter demand, summer risk and operating pressure?
The cleanest way to read the tool is to separate official references, literature-informed simplifications and model-specific calibration. Much of the actual numeric layer belongs to the last two categories, not the first.
| Class | What we take from it | How it enters the model | Confidence |
|---|---|---|---|
| A / PHI | output families, Passive House target values, terminology, core losses-versus-gains logic | reference framework only; not a direct PHPP workbook implementation | high for framing |
| A / ENEA + SIAPE | what APE is, how the A4-G language is used in Italy, and why legal APE is reference-building based | used to frame the public APE-like output honestly, not to compute a legal certificate | high for context |
| A / ECB + ARERA | currency context and editorial energy-price snapshots for the public-facing money layer | presentation and translation layer only | high for source transparency |
| B / architectural research | relative influence of form, compactness, orientation, glazing and shading | used for directional weighting, not blind numerical transcription | medium |
| C / model-specific calibration | surrogate U-values, system efficiencies, market bands, benchmark-house construction archetypes and operating cost assumptions | this is where the public explainer becomes model-specific rather than source-specific | low to medium |
Inputs are normalized first, then converted into idealized geometry, surrogate envelope values, winter losses, winter gains, summer pressure, delivered energy, primary energy, PV effect and finally into readable outputs.
The massing is intentionally idealized into a box-like volume. Here area means total conditioned floor area of the whole house, not the area of one storey. Storeys therefore change footprint, compactness changes aspect ratio, and the envelope area follows from that.
footprintArea = area / stories
aspectRatio = 1 + (1 - compactness) * 1.35
roofArea = footprintArea * (1.06 - compactness * 0.06)
volume = area * 2.6
shapeFactor = envelopeArea / volumeEach facade carries its own glazing share. This is materially better than a single orientation slider, but still not a full solar-geometry model. In the main preset row, the non-passive presets intentionally keep the same benchmark glazing logic; the Passive preset uses one explicit exception with a slightly more south-biased glazing mix on the same benchmark house.
north/east/south/west glazing = 0..60% of facade
windowAreaBySide = facadeAreaBySide * glazingRatio
orientation key = derived from windowSharesThe model does not calculate actual constructions. User-facing sliders are mapped onto surrogate U-values.
Uwall = 0.12 + (1 - insulation) * 1.2
Uroof = 0.10 + (1 - insulation) * 0.8
Ufloor = 0.16 + (1 - insulation) * 0.55
Uwindow = 0.74 + (1 - windows) * 3.0
thermalBridge = 0.03 + (1 - compactness) * 0.14 + (1 - windows) * 0.05The winter balance follows the right conceptual structure: transmission plus ventilation losses against internal and solar gains. Climate is reduced to an HDD-like scalar.
hdd = 1700 + climate * 1100
infiltrationAch = 0.18 + (1 - airtightness) * 0.65
heatRecovery = 0.05 + ventilation * 0.8
ventilationLoss = 0.33 * effectiveACH * 2.6 * HDD * 24 / 1000
internalGains = clamp(2.4 + occupants * 1.05 + appliances * 4.4, 3.6, 13.2)
solarGains = winterSolarBase * windowAreaBySide / area * sideMeta.winterGainAnnual heating demand is one of the strongest outputs in the model. It is also the quantity that sits closest to the classic Passive House heating criterion: about 15 kWh/(m²a) of annual space-heating demand. That is not total delivered energy, not hot water, not appliances and not primary energy. The current public version also adds a calibrated legacy fabric tail correction for the very weak historic end of the range, because the simple slider-based U-value surrogates alone tended to understate how brutal the worst legacy masonry cases feel in practice. Peak heat load is useful as communication, but already more heuristic than the annual balance.
grossHeatLoss = transmissionLoss + ventilationLoss
usefulGains = (internalGains + solarGains) * usefulGainFactor
legacyFabricPenalty = f(very weak insulation, windows, airtightness, ventilation, compactness)
heatingDemand = clamp(grossHeatLoss - usefulGains + legacyFabricPenalty, 5, 420)The summer layer is the most surrogate part of the tool. It captures the right levers, but not a full dynamic comfort simulation.
summerSolarPressure = sum(windowAreaBySide * sideMeta.summerGain)
shadingProtection = sum(windowAreaBySide * shading * sideMeta.shadeHelp)
summerInternalPressure = 2.2 + appliances * 4.8 + occupants * 0.75
summerEnvelopePressure = 1.2 + (1 - compactness) * 3.2 + storyPenalty + insulation * 0.8
overheating = clamp((all summer pressures - protections) * 0.55, 0, 35)The tool is strongest where relative design sensitivity matters and weakest where compliance-grade precision would normally need much richer inputs.
| Output | How much to trust it | Best use | Main weakness |
|---|---|---|---|
| Annual heating demand [kWh/(m²a)] | medium | comparing envelope, windows, airtightness, orientation and compactness | surrogate U-values and climate simplification, plus a calibrated legacy-tail correction for the weakest historic envelope edge |
| Peak heat load [W/m²] | low to medium | communicating how hard the house wants to be heated in cold peaks | not a PHPP heat-load worksheet and not HVAC sizing |
| Summer hours outside comfort [%] | low to medium | showing that glazing distribution and shading can flip the summer result | summer layer is heavily simplified |
| APE-like A4-G label | low | market-facing explanation for the Italian context | not a legal APE workflow |
| Monthly bill translation | low | turning technical outputs into something non-experts can picture | not a tariff quote, not a behavioural model, not a supplier calculation |
This is the part that gives the guide genuine explanatory value rather than random sliders and random numbers.
These are not edge cases. They are the deliberate places where a public explainer chooses legibility over formal completeness.
| Area | PHPP / legal reality | Our simplification | Practical consequence |
|---|---|---|---|
| Climate | specific climate datasets and solar inputs | one climate slider mapped into HDD-like and summer-pressure scalars | absolute numbers are calibration-sensitive |
| Envelope | real constructions and component values | slider-based surrogate U-values plus a calibrated weak-tail correction for legacy masonry | good direction, weaker construction-specific accuracy |
| Thermal bridges | explicit psi-values and junction modelling | one aggregate penalty term | large uncertainty for complex details |
| Ventilation and airtightness | blower-door evidence, schedule logic, unit-specific behaviour | friendly airtightness and ventilation sliders | good trend, weak link to actual n50 and operation |
| Summer comfort | hourly or more detailed logic behind overheating criteria | summer pressure proxy | summer output must be read carefully |
| APE | Italian legal methodology using a reference-building framework | market-facing APE-like translation | useful communication, not legal validity |
The tool is more trustworthy when these limits are said out loud than when they are softened away.
These are the public references that frame the model, the Italian market context and the architectural research layer.
Keček, David. Vliv architektonického konceptu na potřebu tepla na vytápění energeticky úsporných budov pro bydlení [doctoral dissertation]. Brno: Vysoké učení technické v Brně, Fakulta architektury. Available at: dspace.vut.cz/items/ea2121ea-65dd-45a8-b9ae-dd2abd0209fc