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HRV with zoning - How zoned HRV help reduce energy consumption?

zoned HRV ventilation

Since the European Union included home heat recovery units in the scope of the so-called Ecodesign in 2017, the quality of such devices has significantly increased. Manufacturers were obliged to publish reliable data about their products, such as heat recovery value and power consumption, according to the standardized measurement methods.

Product energy labels became a standard, indicating the Energy Efficiency Class and sound power level (noise) that allow the consumer to compare various air handling units. To achieve high-efficiency parameters (appealing to the Customer), manufacturers use energy-efficient fans with EC motors, tight plate heat exchangers with a high percentage of energy recovery, and advanced control automatics.

As a result, Energy Efficiency Classes of modern devices are mostly having the A and A+ labels, have low power consumption, recover more than 90% of heat, and work quietly.

Can we develop them even further?


We have almost reached the limit within the development of equipment itself, but more can be done regarding means of house air supply and establishing ventilation demand.

Imagine a house with a residential area of 130 m2, inhabited by four household members, which – according to the current standards and regulations – will require a total of approximately 265 m3 of air per hour.

This design estimate a ventilation system to supply 265 m3 of air to the entire house, regardless of the external conditions and presence of household members. Of course, users can change the unit efficiency (flow rate) when leaving home and increase it when there are guests in the house. But is this really happening? And are they returning to the previous nominal mode afterward?

The system knows better!


What if that heat recovery uniit would “know” the number of household members and where they stay, providing the right amount of air at the right time and place?

What is zoning?


This way of control is called “zoning”. Zoning, in short, is establishing specific zones at home, where we can anticipate certain behaviors of household members. A typical model divides a house into the day and night zones.

The idea behind such a division is to supply an appropriate amount of air to the area where the household members are present at the moment. During the night, we can ventilate the night zone, e.g., bedrooms located on the 1st floor, and throughout the day the day zone, like the living room and the dining room. The above model of operation may have deviations because some household members may be in their bedrooms, and some may still use the day room.

The system needs a technology for its precise operation to detect the presence of household members, and although it may sound menacing and invasive, it is not complicated at all. In offices, we can obtain data from cameras, thermal imaging, motion sensors, measurement of particular air parameters such as the concentration of carbon dioxide, relative humidity level, or the VOCs, i.e., volatile organic compounds. However, the optimal method of measurement in houses will be the detection of CO2.

What are the additional elements?


Apart from the air handling unit with ducts, such a system will consist of:

  • T-connector with two dampers, a drive, and its automatics
  • 2 x CO2 sensors (1 pc. per zone)

Ventilation zoning

For a proper configuration of the system, proceed as follows:

  • preset the air distribution in the T-connector between zones in accordance with the design, e.g., 50/50 or 60/40;
  • set the maximum CO2 level above which a given zone reading will “determine” the presence of household members (recommended values are 800-1000 ppm);
  • set the minimum air supply to the rooms (the exhaust will always be balanced) in case of the absence of the household members (recommended values are 10-15%);


For ALNOR devices, all communication is maintained via radio waves, so there is no need to make additional wiring.

How does the system algorithm work?


The system continuously measures the air quality (CO2 level) and when household members appear in a given zone, it will distribute the air proportionally to the CO2 concentration readings.

If the ventilation demand in the individual zones varies, the zone with the higher demand will be fully open, and the zone with the lower demand will be partially closed.

When CO2 readings are below 800 ppm, the ventilation demand equals 0%, and the unit supplies the necessary minimum to ventilate an empty house. Accordingly, above 1900 ppm, the demand from the given zone will be 100% until the system detects a decrease of the carbon dioxide level.

The readings generate a proportional increase or decrease of demand and an adequate unit flow rate.

Based on observations, household members occupy half of the house for 63% of the day on average. That gives us the following calculation: 256*0.5*0.63 = 80 m3/h. This means that the flow rate could be reduced by up to 70%! Of course, that is only a theoretical value, but it is possible to reach such flow rates.

Example of the algorithm application using the HRU-PremAIR-350 model:


Design requirement: 256 m3/h
Ratio between zones: 60/40

 Zone 1 Zone 2Unit flow rate 
[m3/h]
Sensor
demand  [%]
Flow rate
[m3/h]
Sensor
demand  [%]
Flow rate
[m3/h]
Case 1 100 102 100 153 255
Case 2 50 56 30 42 99
Case 3 20 29 0 15 44
Case 4 0 10 0 15 25


As presented above, the unit delivers an adequate amount of fresh air where and when you need it. The amount of exhaust air is always proportional to the air supply level.

The zones’ divisions may be different and can be adjusted during the installation as per the Client’s demand.

Decreasing the flow rate of the air handling unit reduces the power consumption and the energy demand for heating. The EU Specific Energy Consumption coefficient indicates possible savings using Mechanical Ventilation System with Heat Recovery.

Class A models (most common) with manual control reach -34 to -42 kWh/m2/year, meaning less energy consumption compared with natural ventilation. Savings may be even greater with the sensor-equipped system and zoning, reaching up to 55 kWh/m2/year.

This way, we can further reduce the annual power consumption up to 20 kWh per square meter.

Calculation example for the HRU-PremAIR-350 model:

VersionSEC 
[kWh/m2/rok]
Household
surface area [m2]
Cost of 1kWh
[PLN]
Annual
savings
15 years’ savings
Manual control -37,78 130 0,3141 -1542,18 -23132,69
Zoning,
local sensors, CF
-55,21 130 0,314 -2253,67 -33805,08

 

Summary


How much has changed in how we control the airflow in our homes! We used to have ubiquitous natural ventilation that only cooled down houses, and there was no reasonable system to control it. Now we have developed advanced systems that can recover 90% of the heat and, at the same time, provide an adequate amount of fresh air to the number of household members.

Would you like to know more? Read other articles on heat recovery ventilation:

  1. How can You install heat recovery unit in the ready-built house?  - the article about decentralized heat recovery systems.
  2. What is an Electrostatic Precipitator and how does it work? - the article about highest filtration efficiency solutions.
  3. 14 Things You Need to Know about PremAIR - pretty self-explanatory title about the best HRU for clients looking for "premium" solutions. 
  4. Air distribution system for the MVHR - overview of FLX-REKU system: radial, semi-rigid ducting, plenum and distribution boxes, etc.
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