Engineering Tool

Single-Room Energy Recovery Ventilator Calculator

Plan rooms with balanced airflow and heat recovery. Review loads, efficiency, supply air, and savings. Make ventilation decisions with practical numbers and visual comparisons.

Use this tool to estimate single-room ventilation airflow, sensible recovery, latent recovery, supply conditions, annual energy benefit, fan energy penalty, and simple payback. It provides an engineering screening estimate for room-level energy recovery ventilator planning.

Calculated Results

These results appear after you submit the form. Export them as CSV or PDF when needed.

Metric	Value	Unit	Notes

This graph compares the untreated ventilation load, recovered energy, fan power, and net recovered power for the entered conditions.

Calculator Inputs

Enter room geometry, ventilation targets, indoor and outdoor conditions, recovery efficiencies, fan power, and economic values.

Room length (m)

Room width (m)

Room height (m)

Occupants

Target ACH (1/h)

Fresh air per person (m³/h)

Indoor temperature (°C)

Indoor RH (%)

Outdoor temperature (°C)

Outdoor RH (%)

Sensible effectiveness (%)

Latent effectiveness (%)

Unit fan power (W)

Operating hours per day

Operating days per year

Conditioned energy rate ($/kWh)

Electricity rate ($/kWh)

Installed unit cost ($)

Example Data Table

This sample shows a typical single-room case for a compact residential or office space.

Parameter	Example Value	Unit	Engineering Note
Room size	5.2 × 4.1 × 2.8	m	Creates a room volume of 59.7 m³.
Occupants	2	persons	Used in the per-person airflow check.
Target ACH	0.7	1/h	Background ventilation requirement.
Fresh air per person	12	m³/h per person	Occupancy-based ventilation requirement.
Indoor / outdoor condition	22°C, 45% / 5°C, 70%	°C, %	Defines sensible and latent recovery potential.
Recovery efficiencies	75 sensible / 55 latent	%	Typical screening values for compact ERV units.
Fan power	18	W	Electrical penalty subtracted from gross recovery.
Economics	0.14 energy, 0.17 electricity, 950 installed	$/kWh, $	Used for annual value and payback.

Formula Used

The calculator uses simplified ventilation and psychrometric relationships for early engineering evaluation. It is ideal for planning, screening, and comparing options before final product selection.

1) Room volume
Volume = Length × Width × Height

2) Airflow from ACH
Flow_ACH = Volume × ACH in m³/h

3) Airflow from occupancy
Flow_people = Occupants × Fresh air per person in m³/h

4) Required design airflow
Flow_required = max(Flow_ACH, Flow_people)

5) Sensible ventilation load
Q_sensible = ρ × c_p × V̇ × |T_indoor − T_outdoor|

6) Sensible recovered power
Q_{sens,recovered} = Q_sensible × η_sensible

7) Outdoor supply air temperature after recovery
T_supply = T_outdoor + η_sensible × (T_indoor − T_outdoor)

8) Humidity ratio
w = 0.62198 × P_v / (P − P_v)
where vapor pressure comes from temperature and relative humidity.

9) Latent recovered power
Q_{lat,recovered} = ρ × V̇ × |w_indoor − w_outdoor| × h_fg × η_latent

10) Net recovered power
Q_net = Q_{sens,recovered} + Q_{lat,recovered} − Fan power

11) Annual net savings
Annual value = Recovered kWh × conditioned energy rate − Fan kWh × electricity rate

How to Use This Calculator

Enter the room length, width, and height.
Add the expected number of occupants.
Set the target air changes per hour.
Enter the fresh air requirement per person.
Type indoor and outdoor temperatures and relative humidities.
Enter sensible and latent effectiveness from the selected unit data.
Provide the fan power and annual operating schedule.
Add local energy and electricity rates for economic screening.
Enter installed cost to estimate simple payback.
Press calculate to view results, graph, and export options.

For final equipment selection, always compare these estimates with manufacturer airflow, pressure drop, sound, frost control, and certified recovery performance data.

Frequently Asked Questions

1) What does this calculator estimate?

It estimates required airflow, sensible recovery, latent recovery, supply air condition, annual recovered energy, fan energy use, net savings, and simple payback for a single-room energy recovery ventilator application.

2) Why does it compare ACH and per-person airflow?

Both methods are common ventilation checks. The calculator uses the larger airflow requirement so the design covers background room air exchange and occupancy-driven fresh air demand.

3) Can I use it for heating and cooling seasons?

Yes. The temperature relationship works in either direction. The tool reports the ventilation load magnitude and the recovered share, so it can screen winter heating or warmer-season cooling cases.

4) Why is latent recovery included?

Energy recovery ventilators can transfer moisture as well as heat. In humid or very dry conditions, this moisture exchange can meaningfully affect comfort, supply air condition, and total recovered energy.

5) Is the supply relative humidity exact?

No. It is a simplified psychrometric estimate based on input temperature, humidity, and latent effectiveness. Final unit behavior depends on core design, bypass control, frost strategy, and airflow balance.

6) What sensible effectiveness should I enter?

Use the certified or published sensible effectiveness for the airflow you expect. If exact data is unavailable, use a reasonable screening range from product literature and compare several cases.

7) Why might net savings become low or negative?

That can happen when temperature or humidity differences are small, operating hours are limited, fan power is high, or utility values are low. Mild climates often reduce energy recovery benefit.

8) Is this enough for final equipment selection?

No. Final selection should also check sound level, pressure drop, installation path, controls, filtration, maintenance access, frost performance, and manufacturer data at the intended operating airflow.