Residential Heat Recovery Ventilation REHVA European Guidebook No 25
REHVA European Guidebook No 25 2 Limited to mechanical supply and exhaust ventilation Targeted to engineers, HVAC consultants and contractors Prepared in cooperation with Eurovent Should include all information and calculation bases needed to design, size, install, commission and maintain HR ventilation properly in order to avoid design and installation mistakes which could destroy the reputation of a dedicated high performance ventilation system Addresses the challenge of silent, clean and draft-free energy efficient HRV that the ventilation should be in modern NZEB
Background 3 In the existing building stock there is less than 1% of heat recovery ventilation (Ecodesign 2010) In new buildings mechanical extraction units (MEU) still dominate the market, but heat recovery units (HRU) share is increasing rapidly (Evia 2017) Residential ventilation in EU building stock, % Heat recovery ventilation, 0.3 Mechanical exhaust ventilation, 16 Natural ventilation with kitchen hood and bathroom fan, 24 No dedicated ventilation, 59
Challenge of silent, clean and draft-free energy efficient HRV Main content Ventilation need selection of airflow rates Ventilation system sizing pressure drop and noise calculations Selection of ventilation units Ventilation system layouts: New buildings Renovation Commissioning and balancing Maintenance
How much ventilation is needed? 5 No consensus in national regulation and guidelines FprEN 16798-1:2016 (EN 15251:2007) and ISO/DIS 17772-1 include new section for airflow rate selection in residences Further developed in this GB to be suitable for practical design Living rooms 2 >15 m 2 Bedrooms >15 m 2 Living rooms and bedrooms 11-15 m 2 Bedrooms <11 m 2, 3rd and the following bedrooms in large apartments WC Bathroom Bathroom in one room apartement Utility room Wardrobe and storage room Kitchen 3 Kitchen 3, one room apartement Kitchen, cooker hood in operation Supply airflowrate L/s 8+0.27 L/(s m 2 ) 14 Average airflowrate of a whole residence L/(s m 2 ) 0.42 Staircase of an apartement building, ACH 0.5 12 8 Extract airflowrate L/s 10 15 10 8 6 8 6 25 Air velocity 1 m/s 1 Maximum air velocity values apply at design airflow rate and supply air temperature in heating season conditions, in boost mode higher velocities may be accepted, see section 2.2. 2 Transfer air from bedrooms may be reduced, 12 L/s is the minimum value 3 Airflow rate in the kitchen when cooker hood is not in operation 0.10 0.10 0.10 0.10
Example: how to determine airflow rates and transfer air paths? 6 The procedure in three and onebedroom apartments are shown in the following slides 1 L/s = 3.6 m 3 /h
Example: one bedroom apartment 7 Airflow rate calculation in one bedroom apartment. The determining airflow rate is marked with bold Room Area, m 2 Airflow rate, L/s (m 3 /h) Supply Extract General air change 2.1 Room 3.0 - - 2.2 Kitchen 9.3-8 (28.8) 2.3 Living room 16.2 12 (43.2) - 2.4 Room 3.7 - - 2.5 Bathroom 3.5-15 (54.0) 2.6 Bedroom 11.5 12 (43.2) - Entire apartment 47.2 - - 47.2 0.42=20 (72.0) Total 24 (86.4) 23 (82.8) 20 (72.0) Total supply and extract airflow rates are almost equal and one extract airflow rate has be increased by 1 L/s to balance the ventilation The total design airflow rate of 24 L/s corresponds to 0.73 ach
Example: 3-bedroom apartment 8 Airflow rate calculation in 3-bedroom apartment. The determining airflow rate is marked with bold Room Area, m 2 Airflow rate, L/s (m 3 /h) Supply Extract General air change 1.1 Kitchen 11.3-8 (28.8) 1.2 Bedroom 11.1 12 (43.2) - 1.3 Bedroom 13.4 12 (43.2) - 1.4 Bathroom 2.8-15 (54.0) 1.5 WC 1.3-10 (36.0) 1.6 Corridor 14.8 - - 1.7 Bedroom 10.9 8 (28.8) - 1.8 Living room 13.6 12 (43.2) - Entire apartment 79.3 - - 79.3 0.42=33 (118.8) Total 44 (158.4) 33 (118.8) 33 (118.8) Extract airflow rates are to be increased: WC 10 L/s Bathroom 15 L/s Kitchen 8+11=19 L/s The total airflow rate of 44 L/s corresponds to 0.80 air changes per hour, which is quite high because of many small bedrooms and expected high occupant density in this 3-bedroom apartment
Ventilation system sizing 9 Selection of supply and extract air terminals Selection of air handling units Ductwork pressure drop calculation Noise and sound transfer in between rooms Fire safety aspects
Air flow rate, l/s Friction pressure losses 5000 1000 10 Specific pressure loss of circular air ducts Dashed lines illustrate the air velocity limits that should not be exceeded to ensure room noise pressures do not exceed 25 db(a) and 35 db(a) respectively 500 100 50 10 5 35 db(a) 25 db(a) 1 0.1 0.5 1.0 5.0 Friction pressure loss, Pa/m
Component pressure losses 11 Manufacturer data to be used If not available, pressure losses may be estimated with default pressure loss coefficients p = ξ ρv2 2
Air velocity limits in supply air ducts of dwellings 12 Recommended maximum velocities and corresponding airflow rates Maximum velocity, m/s Airflow rate at maximum velocity, L/s Ø100 Ø125 Ø160 Ø200 Ø250 Ø315 Air ducts in the apartment after sound attenuators 2.5 20 31 50 79 123 195 Rectangular ducts 3 24 37 60 94 147 234 Circular ducts 4 31 49 80 126 196 312 Circular main ducts 1 5 39 61 101 157 245 390 1 In vertical main ducts of apartment buildings
Example 13 Pressure drop calculation scheme of ductwork L airflow rate, l section length
Section number Airflow rate L,L/s Section length l, m Duct diameter, mm Air velocity, m/s Specific pressure loss, Pa/m Pressure from friction, Pa Dynamic pressure pd, Pa Sum of pressure loss coefficients Σζ, - Pressure drop of ductwork elements, Pa Pressure drop in air terminal, Pa Total pressure drop in section, Pa Ductwork pressure drop calculation table 14 1.1 12 0.3 100 1.5 0.4 0.1 1.4 1.5 2.1 9 11.2 1.2 24 6.0 125 2.0 0.5 3.1 2.3 0.9 2.1 5.2 1.3 44 6.7 125 3.6 1.7 11.1 7.7 1.0 7.7 18.8 1.4 44 1.8 125 3.6 1.7 3.0 7.7 0.4 3.1 16 22.1 Supply ductwork pressure drop 57 Pa 2.1 19 2.0 125 1.5 0.3 0.6 1.4 1.5 2.2 13 15.8 2.2 34 1.0 125 2.8 0.9 1.0 4.6 0.0 0.0 1.0 2.3 44 7.1 125 3.6 1.7 11.7 7.7 2.1 16.2 27.9 2.4 44 1.8 125 3.6 1.7 3.0 7.7 0.3 2.3 5 10.3 Exhaust ductwork pressure drop 55 Pa
Pressure drop ΔP (Pa) Example of a selection diagram of a wall diffuser 15 Pressure drop while fully opened is 6 Pa at design airflow rate 10 L/s The maximum sound pressure of the room is 25 db(a), hence the maximum pressure drop is 30 Pa including a safety margin The maximum pressure drop of the diffuser is 30 Pa The sound pressure limit in living and bedrooms is 25 db(a) The minimum pressure drop of the diffuser is 6 Pa Air flow rate q v (l/s)
Selection of air handling units 16 Supply Nominal size 150 Exhaust L=24 l/s, p=150 Pa SFP=2.17 kw/(m 3 /s), η=80% L=44 l/s, p=150 Pa SFP=2.15 kw/(m 3 /s), η=78% Supply Nominal size 200 Exhaust L=24 l/s, p=150 Pa SFP=1.81 kw/(m 3 /s), η=85% L=44 l/s, p=150 Pa SFP=1.83 kw/(m 3 /s), η=82% Comparison of air handling units at air flow rate 24 and 44 l/s. Pressure drop of ductwork is 100 Pa + 50 Pa of filters. The specific fan power (SFP) is lower, heat recovery temperature efficiency (η) is higher and noise level lower in case of the larger unit
) Sound pressure in room, db(a) Noise calculation 17 Noise calculation is provided, but known as too complicated for many practitioners Alternative method for rough estimation: selection of sound attenuator based on the sound power of ventilation unit at frequency 125 Hz 39 37 35 33 31 29 27 25 23 21 19 17 15 13 Ø225/125 l=600 Ø225/125 l=900 Ø225/125 l=1200 245x185/Ø125 l=1000 45 48 51 54 57 60 Air handling unit sound power @ 125 Hz, db(a) Attenuation, db Attenuator 125 Hz 250 Hz Ø225/125 l=600 Ø225/125 l=900 Ø225/125 l=1200 245x185/Ø125 l=1000 6 13 6 15 6 20 14 19 39 37 Ø260/160 l=600 Attenuation, db
Ventilation units 18 SEC Specific Energy Consumption values as a basis for the labelling and requirements SEC Class SEC in kwh/a.m 2 A + (most efficient) SEC < -42 A -42 SEC> -34 B -34 SEC>-26 C -26 SEC>-23 D -23 SEC>-20 E -20 SEC>-10 F -10 SEC>0 G (least efficient) 0 SEC SEC, calculated for average climate, shall be no more than 20 kwh/(m 2 a) after 1 Jan 2018
19 SEC (kwh/(m 2 a)) represents the specific (primary) energy consumption for ventilation per m 2 heated floor area. The equation, written for the mandatory average climate, includes three parts: Fan electricity calculated with 8760 operation hours, primary energy factor 2.5, ventilation rate 1.3 m 3 /(h m 2 ), SPI in kw/(m 3 /h) units, 1.1 parameter for bidirectional ventilation units and control parameters from Table 4.2; Heat recovery saving relative to reference natural ventilation rate of 2.2 m 3 /(h m 2 ) that is calculated in an average climate for a 5112 h heating period with an average indoor to outdoor temperature difference of 9.5 K, space heating efficiency 0.75 and specific capacity of air 0.000344 kwh/(m 3.K); Frost prevention energy Q defr, i.e. to heat outdoor air up to -4 C that is equal to 0.45 kwh/(m 2 a) for recuperative heat exchangers and 0 for regenerative heat exchangers
SEC Specific Energy Consumption 20 For example, with a temperature ratio of 0.8 and SPI =1.5 kw/(m 3 /s) = 0.000417 kw(m 3 /h) results in SEC = -29 in the case of manual control and multi-speed (class B) In the case of local demand control and variable speed SEC = -37 (class A) To reach the best possible class A+, SPI = 0.9 kw/(m 3 /s) = 0.00025 kw(m 3 /h) and a temperature ratio of 0.9 are needed together with local demand control and variable speed. In the case of regenerative heat exchangers SPI = 1.0 kw/(m 3 /s) would be enough for class A+
Heat recovery temperature ratio 21 Where t 22 is supply air outlet (supply); t 21 is supply air inlet (outdoor); t 11 is extract air inlet (extract); t 12 is extract air outlet (exhaust); q m22 is supply air mass flow; is extract air mass flow; q m11 two types of heat exchangers are used in residential ventilation units, plate heat exchangers (recuperative) and rotary heat exchangers (regenerative)
Counterflow plate heat exchanger 22 The supply air and extract air have completely separate air passages therefore any possible odours in the extract air do not transfer to the supply air Plate heat exchangers (of metal) do not transfer humidity and are more sensitive to frosting Under specific temperature and humidity conditions condensation can occur in the heat exchanger on the exhaust side and it has to be safely drained outside ventilation unit
Rotary heat exchangers 23 Rotary heat exchangers (non-hygroscopic and hygroscopic) transfer humidity due to condensation and are less sensitive to frosting Humidity transfer is a positive feature in a cold climate as it can help avoid excessively low relative humidity in the winter While rotary heat exchangers are recommended for a cold climate, in very small apartments with high occupant density, where humidity removal becomes important, non-hygroscopic heat exchangers are recommended
Filters 24 Minimum particle removal efficiencies (e min PM) in ISO filter classes are shown in the Table below Particle removal efficiency shows the percentage of particle mass in the air removed by the filter. Removal efficiencies are defined for smaller and larger particle size ranges, i.e. up to 1 µm (ultrafine), up to 2.5 µm (fine particulate matter, the most important size range) and up to 10 µm (very large particles/coarse dust) ISO 16890 Filter Classes e min PM 1 e min PM 2.5 e min PM 10 Reporting Value ISO Coarse <50% Arrestance ISO PM 10 >50% epm 10 ISO PM 2.5 >50% epm 2.5 ISO PM 1 >50% epm 1
Ventilation system layouts 25 Ventilation units typically installed in bathrooms, on the top of cooker hoods or in the service spaces or attic Main focus to centralized and decentralized ventilation systems Some warnings regarding room ventilation units (monoblock), which have been problematic especially in renovation Specific solutions for renovation best practice examples collected
Typical single dwelling ventilation unit 26 Plate heat exchanger: cooker hood extract is taken through the heat exchanger Rotary heat exchanger: and these units incorporate an extra duct connection for the cooker hood by-pass (i.e. connected after the heat exchanger) Outdoor air is taken directly from the facade, but exhaust is ducted to the roof
Cooker hoods in modern buildings 27 Separated cooker hoods can generate more than 100 Pa negative pressure in new airtight dwellings it is preferable to connect the cooker hood to the ventilation unit in order to allow balanced operation If not compensated, then the maximum negative pressure during cooker hood operation should not exceed 30 Pa 5) 7) 2) 4) 1) 6) 3)
Airflow balance in airtight buildings 28 Nearly zero energy buildings nzeb = airtight buildings with n 50 < 1 1/h Special solutions needed for cooker hood and fireplace compensation
Single dwelling ventilation unit integrated with the cooker hood 29 Brown arrow on the wall (optional) indicates that in some cases exhaust through the wall is possible where, particuarly in that case, distances to windows and minimum velocity as well as compliance with local requirements is to be checked
Centralized system Plate heat exchangers are always used to avoid odour transfer in the heat recovery section Air handling unit serves cooker hoods and constant pressure is maintained halfway between that of the supply and extract air main ducts Opening the cooker hoods will increase extract airflow rate in the dwellings and the system increases the fan speed in order to keep constant static pressure in the main ducts
Typical pressure drops 31
Cooker hood operation 32 In centralized system on/off damper and an additional supply air diffuser controlled with voltage signal General ventilation (min 8 L/s constant airflow) and boost (min 25 L/s) when the damper is opened
Cooker hood operation range 33 The switch on the left opens the damper and the switch on the right is for the light
Renovation 34 Centralized ventilation system installation in renovation Supply and extract ducts are installed into existing shafts
Renovation: installation out of building 35 Installation of supply air ductwork in the insulation layer on the roof on the left and with flat ducts in the façade on the right Centralized air handling unit on the top of the roof on the left and the building after deep renovation on the right
Renovation: main installations placed in the hallways 36
Renovation: Installation example with acoustic damper box and distributor 37
Ductwork installation in renovation 38
Commissioning 39 Procedure how to adjust the system and air diffusers: Start adjusting duct branch B, since this one has the highest ratio (quotient) of K=1.11 The last air device, B3, has the lowest ratio of K = 0.9 and should be fully open. Adjust the other air devices, B1 and B2, so that these will have the same ratio as air device B3 branch duct C branch duct A When commissioning has been completed, 3 air devices and one branch damper should stand fully open to obtain the lowest possible pressure in the system
Maintenance 40 Filters Heat recovery unit Ducts and Accessories Air terminals Air intakes and exhausts