If you are planning to build your own house, you will need ventilation with a heat recovery and a bunch of sellers will praise their products. The most of them will point out fantastic amount of energy you will save and will not bother to tell that there is Commission regulation (EU) No. 1253/2014, which requires to provide unit data according to certain conditions, not to theoretical 95% efficiency. Even by providing the data sellers won’t tell that Eco-design data is calculated and not measured at the most cases, therefore some manufacturers give “nicer” numbers. And there is no actual body in the most part of the EU which can and want to check it. In this article I will use official data for AHU manufacturers: SALDA, Komfovent, FLEXIT. The reliability remains a matter of their conscience.
First, air handling unit is an electrical appliance which uses electrical energy to generate air movement and in certain cases to heat up the supplied air.
Components that use electrical energy
Every air handling unit has these internal components which consume electrical energy:
Nowadays efficient EC fans are installed in residential heat recovery units and consume relatively low amount of energy.
- Air heater
An AHU has an air heater because the heat exchanger does not return the full amount of heat and supply of cool air may have negative effect on indoor climate. In household ventilation units an electrical heater is the most common due to lower installation costs and better serviceability. The more powerful air handling unit is and the less efficient heat exchanger is installed the more powerful heater is needed.
- Air pre-heater
An air preheater is used for the heat exchanger frost protection. In a moderate climate zone, it is required only for the protection of plate heat exchanger. In northern Germany preheater will be required to have enough power to heat up outdoor air for dT=11C, Poland – dT=19C, even max power will be used rarely.
- Rotor drive.
Rotor motor spins rotor and uses quite insignificant amount of energy, therefore I will not include it in a calculation.
- By-pass damper actuator
By-pass damper is used quire rarely therefore it is not included in calculation.
For the calculations I will use technical data from Eco-design technical data sheets from manufacturers websites.
The compared models:
- SALDA: Smarty 2R VE, RIRS 400 VE EKO 3.0 and Smarty 3XP
- Komfovent: Domekt R 200 V, Domekt R 400 V and Domekt CF 400 V
- FLEXIT: UNI 2 and UNI 3.
Smarty 2R V
Domekt R 200 V
RIRS 400 VE EKO 3.0
Domekt R 400 V
Domekt CF 400 V
Max airflow rate at 100 Pa
Max power input of both fan drives, kW
Max. power input of heater, kW
Pre-heater (integrated or recommended), kW
Reference flow at 50 Pa
Fans power consumption at a reference point, kW
Efficiency of heat recovery at the reference point, %
Maximal air flow of the heat recovery units vary from 201 m3/h up to 428 m3/h and are dedicated for ventilation of premises from a small sized apartment up to an average sized house. All of them have integrated electrical heating devices, except Smarty 3XP.
One of the most important indicators is SPI (specific power input) shows how much do the fans use energy at the reference point for transportation of 1 m3/h of the air.
Heat recovery efficiency indicates how much heat is recovered from the extracted air.
The more efficient heat recovery is, the less energy is needed for air post-heating.
EU requests to provide AEC factor, which indicates theoretical energy consumption of the ventilation unit for the 100 sq. m of the heated floor area.
It seems Komfovent has the best rate, but in general I am not fully convinced of their data.
Energy for the air movement
Fans are essential component of every ventilation unit. Modern EC-type fans consume quite low amount of electricity. But because they operate all year round, they use about the same amount of energy monthly. The power of fan must be enough to overcome resistance of the ventilation system and the internal resistance itself. Internal resistance depends of the internal components: filters, heat exchanger, heaters etc. The more efficient filters are (or more contaminated), or the more efficient heat exchanger is, the higher internal pressure drops are, and the more powerful fan is needed. For calculation of energy consumption, I have taken reference point according to Eco-design, which is 70% of maximal airflow at 100 Pa.
In this case, if the unit works constantly, monthly energy consumption is as follows
Energy for air heating
Energy for air heating consists of energy for supply air heating and outdoor air pre-heating.
As I have previously pointed, quantity of energy for the supply air heating depends of the efficiency of the heat recovery device. The more efficient heat recovery is the less energy is needed for the heating to the requested temperature.
For example, in the northern Poland average temperature in January is -5C, in the room is +22C.
Temperature after heat exchanger at this case:
As we can see from the chart, temperature after heat recovery device in January is between 13C and 20C. If we require supply air temperature of 20C, we need to heat up the air accordingly.
For the air handling unit with plate heat exchanger as Smarty 3XP and Domekt CF 400 V, preheater for frost protection is needed. According to the technical data it is necessary to heat it up at least up to -3C. If the air temperature in the middle of January is below -10C, then we need to heat up the air for dT=7C.
In winter time for the air heating it may require from 160kWh up to 360 kWh of electrical energy in such climate zone.
Total energy expenses
In total it will be such energy consumption of your ventilation units.
Average electricity prices in EU are about 0.20 EUR per 1 kWh:
Of course, Denmark citizens may face 50% higher expenses due they have most expensive energy in EU.
But don’t be afraid of such a high expense. Such units of such manufacturers as SALDA, Komfovent and FLEXIT have a lot of smart functions of energy savings as calendar mode etc. Therefore, ventilation rate will be reduced when you are leaving the house.
I received testing date of the long term run test from the one of manufacturers. In 2017 November-January, unit was switched on only occasionally therefore data at this period differs.
At this case energy costs will be as follows:
Air handling units’ energy expenses are the highest in winter. Therefore, don’t be surprised that it will consume 160-300 kWh of electrical energy and will cost additionally 40 € to 90 €. In summer time it will not be higher than 15 €.
How to spend less:
– Before buying of the unit, please pay attention to technical details of the desired ventilation unit;
– Check the type of electrical heater control. 0-10V controlled heater will use up to 20% less energy for heating;
– Buy ventilation unit only of reliable manufacturers. Check if they have certification and tested at the external testing labs;
– Check the ventilation calendar. If you are not home at the certain time, adjust ventilation speed to minimal and reduce air heating.
– And of course, change filter on time! Contaminated filter lead to the higher pressure drops and the higher energy consumption of the fans. P.S. All the calculations are provided to the units with clean filters 🙂