RENBEM · USER GUIDE

RenBEM Help & Documentation

Learn how to use RenBEM v1.1, the free preliminary building heating and cooling load estimator. This guide explains the inputs, location-based climate estimates, peak-load results, 24-hour analysis, calculation method, and current limitations.

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v1.1 Hourly previewBrowser-based CalculatorCSV ExportFree To use

1. Quick start

You can calculate a preliminary peak heating and cooling estimate in a few steps. Start with the building inputs, select a location if you want climate estimates, then review the load breakdown.

Enter the building basics. Set the conditioned floor area, conditioned volume, and indoor heating and cooling setpoints.

Choose a location. Search for a city or use your browser location. RenBEM retrieves historical outdoor temperature data and suggests winter and summer design estimates.

Review the envelope. Enter wall, roof, floor, and window areas with their U-values. Add glazing SHGC, peak solar irradiance, and external shading.

Set occupancy and outdoor air. Enter design occupancy, ventilation per person, infiltration, lighting, equipment, and humidity-ratio difference.

Calculate loads. Select Calculate loads. Review peak heating and cooling loads and their component breakdowns. Use Export CSV to save the estimate.

Run hourly analysis (optional). With a location selected, choose an available historical date and select Analyze 24 hours.

Tip: Keep the same assumptions when comparing alternatives. Change one or two inputs at a time so you can see which building feature drives the result.

2. Location and climate estimates

Search for a city

Enter a city or address and select Search. RenBEM uses the Open-Meteo geocoding service to resolve the location. It then requests historical daily minimum and maximum temperatures from the Open-Meteo Archive API.

How outdoor design estimates are derived

The calculator uses approximately ten years of historical daily temperature data, ending seven days before the current date. It estimates the winter outdoor temperature from the 1st percentile of daily minimum temperatures and the summer outdoor temperature from the 99th percentile of daily maximum temperatures. Values are rounded to the nearest 0.5 °C and placed in the outdoor design fields.

Use my location

This option asks your browser for location permission. If you decline or location services are unavailable, search for a city instead. The location must be selected again after using Reset defaults.

Important: These are statistical climate estimates, not official project design conditions or code-prescribed design temperatures. Review and replace them with appropriate local design data for engineering work.

3. Parameters explained

The following table reflects the current RenBEM v1.1 controls and their starting values. Numeric fields are editable; where a minimum is shown, values below it are rejected.

Parameter	Unit	Default	Purpose
Conditioned floor area	m²	250	Floor area used for internal gains and W/m² reporting.
Conditioned volume	m³	750	Used with infiltration air changes per hour to calculate outdoor airflow.
Indoor heating setpoint	°C	20	Heating indoor reference temperature.
Indoor cooling setpoint	°C	26	Cooling indoor reference temperature.
Outdoor winter design estimate	°C	−5	Outdoor reference for peak heating; can be auto-filled and edited.
Outdoor summer design estimate	°C	35	Outdoor reference for peak cooling; can be auto-filled and edited.
Ground temperature	°C	10	Reference temperature for ground-floor heat loss.
External wall area	m²	180	Opaque external wall area, excluding windows.
Wall U-value	W/m²·K	0.35	Thermal transmittance of external walls.
Roof area	m²	250	Area of the roof exposed to the modeled boundary condition.
Roof U-value	W/m²·K	0.25	Thermal transmittance of the roof.
Ground floor area	m²	250	Area used in the simplified ground-floor heat-loss term.
Floor U-value	W/m²·K	0.40	Thermal transmittance of the ground floor.
Window area	m²	40	Glazing area used for conductive and solar gains.
Window U-value	W/m²·K	1.40	Thermal transmittance of the glazing.
Glazing SHGC	0–1	0.55	Fraction of incident solar energy admitted as heat.
Peak solar on glazing	W/m²	450	Peak irradiance applied to the glazing solar-gain estimate.
External shading factor	0–1	0.70	Multiplier for solar gain; 1.0 means no reduction and lower values mean stronger shading.
Design occupancy	People	12	Used for ventilation and occupant heat gains.
Outdoor air per person	L/s/person	10	Ventilation flow assigned to each occupant.
Infiltration	air changes/hour	0.50	Infiltration airflow based on conditioned volume.
Lighting load	W/m²	8	Internal lighting heat gain per floor area.
Equipment load	W/m²	10	Internal equipment heat gain per floor area.
Humidity-ratio difference	g/kg	6	Used to estimate the latent outdoor-air cooling load.

Understanding U-values

A U-value describes how readily heat passes through a building element. Lower U-values generally indicate better thermal insulation. Use values that represent the complete construction assembly where possible, not just one material layer.

Understanding SHGC and shading

Solar heat gain coefficient (SHGC) represents the fraction of incident solar energy that enters through glazing as heat. The shading factor reduces the modeled solar gain. Both inputs must be between 0 and 1.

4. Understanding the results

Peak heating load

The estimated heating rate required under the entered winter conditions, shown in kW thermal. Its breakdown includes walls, roof, windows, ground floor, and outdoor air.

Peak cooling load

The estimated total cooling rate, including sensible and latent components, shown in kW. Its breakdown includes envelope conduction, window solar gain, people, internal loads, and outdoor air.

Specific load

Heating or cooling load divided by conditioned floor area, shown in W/m². This helps compare estimates for buildings of different sizes but does not replace a detailed design calculation.

Load breakdown bars

Each bar shows the relative share of a component in the corresponding total. Component values are displayed in kW and help identify the largest modeled contributors.

Exporting results

Select Export CSV to download a spreadsheet-compatible file containing the calculated totals, specific loads, outdoor airflow, component values, and a note describing the preliminary scope. The export is created from the current valid inputs.

Check the units: kW is a rate of heat transfer (load). kWh is energy accumulated over time. RenBEM estimates peak loads; it does not calculate annual building energy consumption.

5. 24-hour load analysis

RenBEM v1.1 adds an optional hourly profile for one selected historical day. It uses hourly outdoor temperature and shortwave solar-radiation data from the Open-Meteo Archive API and applies the current building inputs to each hour.

Select a location first. Search for a city or use your location and wait until the climate data has loaded.

Choose a date. The date control allows historical dates from 1 January 2010 up to seven days before the current date. Data availability varies by location.

Analyze 24 hours. Select Analyze 24 hours. The calculator requests hourly outdoor temperature and solar radiation for that date.

Review the profile. The summary shows the peak hourly heating and cooling estimates. The chart compares hourly loads, and the table lists outdoor temperature, solar radiation, heating, and cooling for each hour.

How to interpret hourly values

Each hour is a separate simplified steady-state estimate using that hour’s outdoor temperature and solar radiation. Occupancy, ventilation, lighting, equipment, and the other building inputs remain constant for all 24 hours. The hourly profile is useful for exploring how weather changes the indicative load, but it is not a simulation of how the building’s temperature or thermal mass evolves through the day.

24-hour preview limitations: Thermal mass, solar orientation, shading schedules, occupancy schedules, HVAC control sequences, and dynamic heat storage are not modeled. It is not an 8,760-hour annual simulation and does not calculate annual energy use.

6. Calculation method

RenBEM is a single-zone, preliminary peak-load estimator. It combines simplified envelope heat transfer, outdoor-air loads, glazing solar gain, and internal gains.

Outdoor airflow
Ventilation (m³/h) = people × outdoor air (L/s/person) × 3.6
Infiltration (m³/h) = air changes/hour × conditioned volume
Total outdoor airflow = ventilation + infiltration

Envelope transmission
Q = U × A × ΔT

Outdoor-air sensible load
Q ≈ 0.33 × airflow (m³/h) × ΔT

Window solar gain
Qsolar = window area × peak solar irradiance × SHGC × shading factor

Outdoor-air latent load
Qlatent ≈ 0.83 × airflow (m³/h) × humidity-ratio difference (g/kg)

Heating sums transmission losses through walls, roof, windows, and ground floor with outdoor-air sensible losses. Cooling combines envelope conduction, glazing solar gain, occupant sensible and latent gains, lighting and equipment, and outdoor-air sensible and latent loads. The current model assumes 75 W sensible and 55 W latent heat gain per person.

7. Scope and limitations

RenBEM v1.1 is a simplified single-zone peak-load estimator with a 24-hour sequence of steady-state estimates for a selected historical day. It is not standards-compliant design software and is not a full dynamic building energy simulation.

It does not calculate annual energy use or an 8,760-hour annual profile.
It does not model thermal mass, dynamic heat balance, or moisture buffering.
It does not resolve detailed solar position, façade orientation, or time-varying shading.
It does not model thermal bridges, detailed ground coupling, or construction-layer heat storage.
It holds occupancy and internal gains constant in the hourly analysis.
It does not model HVAC equipment efficiency, control sequences, or system sizing procedures.
Location-based outdoor temperatures are statistical estimates, not official design conditions.

Engineering caution: Do not use the result alone to size equipment, prepare permits, make procurement decisions, or guarantee performance. Final design requires suitable design conditions, room-by-room calculations, applicable standards, and review by a qualified building-services engineer.

8. Troubleshooting

City search does not work

Check your internet connection and try a simpler city name. If an address is not found, search for the city or nearest town instead.

Climate data does not load

The geocoding or historical weather service may be unavailable, or the location may not have the requested data. Try again later or enter outdoor design temperatures manually. Your manual values remain editable.

Calculate loads shows an input error

Check that every numeric field contains a valid number, floor area and volume are greater than zero, and SHGC and shading factor are between 0 and 1. Review the field values and calculate again.

Hourly analysis does not run

Make sure a location is selected, the date is within the available range, and the historical weather service returns a complete 24-hour record. Try another date if hourly data are missing.

Results look too high or too low

Review the design temperatures, envelope areas and U-values, outdoor airflow, glazing solar inputs, occupancy, and internal gains. Confirm that you have entered the correct units and that the assumptions represent the building.

9. Frequently asked questions

Is RenBEM free?

Yes. RenBEM is a free, browser-based preliminary heating and cooling load estimator.

Does RenBEM save my building data?

The current calculator runs in your browser and does not send or store the entered project values on Renwaves servers. Location searches and weather requests are sent to Open-Meteo services.

Can I use RenBEM to select a heat pump, boiler, or chiller?

Use the result for early screening only. Final equipment selection requires a complete design calculation, room-by-room loads, operating conditions, manufacturer data, and applicable local standards.

Does v1.1 perform dynamic hourly simulation?

No. It calculates 24 separate steady-state estimates using hourly weather for one historical day. It does not simulate thermal mass or changing indoor conditions.

Can I calculate annual energy use?

No. RenBEM v1.1 estimates peak loads and a selected-day hourly profile. It does not calculate annual energy consumption or an 8,760-hour annual profile.

What is the difference between heating load and cooling load?

Heating load is the rate of heat that must be added to maintain the heating setpoint. Cooling load is the rate of heat that must be removed to maintain the cooling setpoint. Both are reported in kW.