HVAC Heat Loss & Cooling Calculator

Insulation level Step 1

Building details

Building type

Construction year

Design outdoor temp — winter (°C)

Ventilation rate (ACH)

MVHR heat recovery eff. (%)

Thermal bridge correction ?

Design outdoor temp — summer (°C)

Indoor cooling setpoint (°C)

Location (Bulgarian city)

Ground floor heat loss method

Use ISO 13370 (slab-on-ground) — more accurate for ground-floor rooms

When unchecked, a simplified U×A×ΔT method is used with U_floor from the insulation preset.

Solar shading (summer cooling)

How shading inputs work:


Roof/balcony edge
    ├──── overhang depth ────┤
    │                        ↓ (edge of overhang)
    │ ← window top           ╌╌╌╌╌╌╌╌
    │                        ↑ window-to-overhang height
    │ ← window               (gap between top of window and underside of overhang)
    │
Floor

Overhang depth = horizontal projection of the overhang (roof edge, balcony floor, sunshade). E.g. 0.6 m = balcony extends 0.6 m beyond the wall face.
Window-to-overhang height = vertical distance from the top of the window to the underside of the overhang. Smaller = more shading.
Only applied to south-facing walls (S). E/W walls receive partial effect. N walls: no solar benefit from overhangs.
Blind/shutter factor is multiplied on top: 1.0 = no blind, 0.25 = external roller shutter blocking 75% of solar.

Overhang depth (m) — horizontal projection

Window-to-overhang gap (m) — vertical

External blind / shutter

Floor bounding box & orientation

Max building width (m, E–W)

Max building depth (m, N–S)

North direction (°, clockwise from up)

Grid snap

The bounding box appears as a dashed rectangle on the canvas — rooms must fit within it. North angle rotates the compass and affects wall orientation for solar gain calculations.

Floors 1 floor

Each floor has its own set of rooms and canvas. Switch floors using the tabs below. Rooms on all floors are included in results.

Floor plan canvas interactive

━ Red = exterior wall · Right-click any edge to set wall type or mark/unmark as exterior · Move: drag room · double-click name to rename · double-click ↔ label to edit value · Edit shape: drag vertices (○) · click midpoint (·) to add vertex

Rooms 0 rooms

Thermal inertia (mass) effect RC model

Apply thermal mass damping to main peak loads Off by default. EN 12831 sizes plant on steady-state design conditions and allows no diurnal mass credit — design cold spells last days, not hours, so the swing this models has already died out by the time the peak matters. Tick it to see the damped figures, but size equipment on the undamped ones unless you have a specific reason not to.

This model treats the building as a resistor–capacitor (RC) circuit. Thermal mass stores heat and delays temperature swings, reducing both the peak heating demand and peak cooling demand compared to a steady-state calculation.

Thermal mass class

Effective time constant τ (hours)

Auto-estimated from inputs — override if needed

Daily temp swing amplitude (°C)

Typical daily peak-to-trough swing

How it works: The RC model computes the transfer function of a 1st-order thermal system with time constant τ = C_m×A / (ΣUA + ventilation conductance). For a sinusoidal outdoor temperature with amplitude A and period T=24 h, the indoor amplitude is attenuated by the factor 1/√(1+(2πτ/T)²). This attenuation is applied to the peak loads to estimate the demand reduction from thermal mass. It is a simplified, indicative model — not a substitute for dynamic simulation.

Energy bills Step 4 (optional)

Have historical gas/electricity/etc. bills for this building? Enter a few billed periods below and this tool will reverse-engineer a probabilistic estimate of the REAL insulation level from them — a cross-check on the preset guess on the Insulation step, not a replacement for it.

Your contact details Step 5

First name *

Last name *

Email *

Phone

City / municipality

Preferred contact method

Notes / questions

Your project data (including floor plan and calculations) will be sent securely to Voraggo along with this request.

✓ Request submitted

Your enquiry and full building data have been sent directly to info@voraggo.com.

The JSON project file was attached automatically.

We will contact you within 1 week with a detailed assessment and recommendations.

🏠 HVAC Heat Loss & Cooling Calculator

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