How to acquire Demand Controlled Ventilation with energy optimal functionality? John Woollett CEng Reserachers from SINTEF; Mads Mysen & Peter Schild

Transcription

1 How to acquire Demand Controlled Ventilation with energy optimal functionality? John Woollett CEng Reserachers from SINTEF; Mads Mysen & Peter Schild 1

2 John Woollett C.Eng, F.CIBSE, F.REHVA, M.ASHRAE. Working for Swegon for 12 years HVAC life; Research an Development Air Handling Units. Swegon Air Academy. Demand Control Ventilation system, air and waterborne. Chilled beam guidebook for REHVA / ASHRAE. Support to Swegon UK in London.

3 Points to cover 1. Define Demand Controlled Ventilation. 2. Why it is important energy policy. 3. What our professional can do about it. 4. Practical Application / understanding of DCV. 5. Sensor types. 6. Commissioning. 7. Documenting projects. 8. How DCV can help basic EPC.

4 What is Demand Control Ventilation What makes DCV different EN standards A ventilation system where the ventilation rate is controlled by air quality, moisture, occupancy or some other indicator for the need of ventilation.

5 Definition of DCV Provide the exact amount of clean air at the required temperature at the right time in the right place. Source:Maripuu, Chalmers

6 Climate change and energy policy IPCC: 50% reduction against 1990 levels of manmade CO2 emissions before EPBD Recast Renovation existing buildings. Near Zero Energy buildings (NZEB) by Ventilation constitutes a major share of the total energy use buildings of existing non-commercial buildings in the Nordic countries, typically 35-50% for office buildings.

7 Why DCV? Majority of European building stock is here. How many are suitable for large lower pressure ducting system? How many new buidings? Use technology to solve an existing problem. Efficient use of energy: YES Compromise on IAQ? NO The use of CAV, unless it is source ventilation is questioanble, as it adds not benefit to the IAQ.

8 8 Demand Controlled Ventilation

9 SFP e N i 1 N i 1 Pi q v, i t t i i SFP and airflow N i 1 SFP e, i qv, i ti N q t i 1 v, i i 1 Fraction of max SFP Poor Normal Good Ideal r ² r, Fraction of maximum flow rate Needless throttling along the critical path.

10 SFP and energy use for fans

11 Energy use CAV Fan energy m³/h 1h kw h m² 3600s m³/s yr Heat energy 17 kwh m² yr m³/h 1 h 10 3 o C 1000 m² 3 yr 10 kwh m² yr

12 Control against a pressure setpoint Pressure sensor 2/3 out on the main branch The fan speed drive is controlled by the pressure sensor in the main ventilation duct. 12

13 Fraction of max SFP Poor Normal Good Ideal r ² SFP=2*0,4 SFP=2*0, r, Fraction of maximum flow rate SFP=2*0,8

14 CAV SFP and energy at r = 0.8 m³/h 1h kw h m² 3600s m³/s yr m³/h 1 h 10 3 o C 1000 m² 3 yr kwh 10 m² yr kwh 17 m² yr Constant pressure inaccurate sensor/ bad sensor placement r-control =0,8 m³/h 1h kw h kwh 8 1, m² 3600s m³/s yr m² yr m³/h 1 h kwh 8 3 o C m² 3 yr m² yr

15 CAV SFP and energy at r=0,6 m³/h 1h kw h m² 3600s m³/s yr m³/h 1 h 10 3 o C 1000 m² 3 yr Ideal control m³/h 1h kw h 6 0, m² 3600s m³/s yr m³/h 1 h 6 3 o C 1000 m² 3 yr kwh 6 m² yr kwh 17 m² yr 10 kwh 4 m² yr kwh m² yr

16 Experiences from pressure control (Klæboe og Hermann 2011) Surveys show systematically higher fan energy with pressure control than SPR ( Mingsheng Liu et al., 2007) and active terminal diffusers ( Maripuu 2009) Often problematic function ( Allegrini 2010) Sensor does not capture change - Only redistribution One reason - unfavourable positioning of pressure sensor Stable pressure and developed velocity profile (not around a corner) The correct position varies Pressure sensor must be placed far out, but no definitive how far. 16

17 Real life experiences from pressure control

18 Real life experiences from pressure control

19 Real life experiences from pressure control

20 Real life experiences from pressure control X? X X

21 21 Damper controlled

22 Controlling towards the optimal pressure P s P s P s P s

23 Digital DCV Only occupancy is reported back 23

24 24 Real life

25 Experiences from Digital Demand Controlled Ventilation Solutions are need that give: compensates for errors and / or failure notifications that this channel leak provide evidence of real delivery (employer's liability in relation to air quality is safeguarded) easily modify airflow can supply different minimum levels depending on whether within normal working hours or not. 25

26 DCV-potential - % of CAV 75 % 70 % % of CAV kwh/yr 65 % 60 % 55 % 50 % 45 % 40 % 35 % 30 % 25 % Energy use DCV-IR Energy use CAV Energy use DCV-CO 2 Energy use CAV T op [hours]

27 Sensor types Source: SINTEF

28 Requirements CO2-sensors Measurement uncertainty Lifetime Calibration Procedure Delta Controls inside - outside sensor ( EN ) Control ( requirements - measurement uncertainty ) location Function control with BMS 28

29 Minimising deviations theory / practice with better control Final check Function control at room level. Function control at zone level. Function control at AHU level. SFP shall be measured and documented By knowing the operating status, full visibility and reduced maintenance. Be realistic with the work schedule regarding the final phase. After 1 yr follow up inspection Having a predetermined mutual compensation for failure to meet requirements such as related energy costs.

30 The load tests Max-max-min and Min-min-max

31 The load tests Max-max-min and Min-min-max Max-max-min 1. Put all the DCV diffusers to max air flow at the same time in the zone worked on, so the zone s max air flow is delivered by the AHU. All other to min air flow. 2. Record max airflow on supply and exhaust in all rooms at max air flow. 3. Record min airflow on supply and exhaust in all rooms at max air flow. 4. Repeat for all other zones. Min-min-max 1. Force control all DCV units in the building to Vmin. 2. Record min airflow on supply and exhaust in all rooms at max air flow. 3. Record max airflow on supply and exhaust in each room.

32 Calculation example You have signed an EPC contract with SFP = 2. A deviation compensated both ways similar difference in fan energy for 10 years with an energy price of $ 1 / kwh You delivered a plant with SFP = 1.6. The plant is 10,000 m3 / h and the running time is 3000 hours. How much should the builder pay your firm? 32

33 SFP and energy use for fans m3/h 3000 hours of operation m³ 1h kw h (2 1,6) 3000 h 3600s m³/s yr kwh 3333,33 yr You will have; 10x3333= costs

34 Better demand control Better management requires better demand and control! Se Fraction of max SFP Poor Normal Good Ideal r ² r, Fraction of maximum flow rate Control of capacity Control of energyefficiency Relationship between change in room airflow and AHU airflow Always one open DCV-damper

35 Documentation To be able to run a DCV project all the way with maximum energy saving, it is important to put some effort into the documentation.

36 Documentation Ventilation plan must contain: All levels of airflows; unoccupied minimum occupied maximum occupied (for example l/s). Pressure sensor placement must be on plan. Individual marking to each components. Type Size - room number (for example SP ). Function of zone dampers. This can be done at each individual or in a table placed on the ventilation drawing.

37 Documentation plan example

38 Documentation We have to think in a larger perspective, we must not only understand the system today and tomorrow, but even in ten years time we should be able to read the drawings and understand the functions.

39 DCV tips Start DCV planning from the first step. Which room shall have balanced supply and extract air, or supply and transfer air? Which room shall have DCV or CAV? How shall we solve the main ducting / shafts (vertical and horizontal)? Dimensioning of system and air handling unit(s)

40 Wish list More smart functions as self-optimisation, for both temperature and pressure. Weather-control system for energy-optimised buildings. Technological boost in the design software as: CAD software that can simulate and calculate DCV. IAQ indicator? Greater focus on simplicity.

41 Conclusion Design for DCV from the beginning. Consider future changes of the system in the building. A practical understanding of air flow and pressure is needed when making changes in DCV systems.

42 DCV IS EASY REDUCES ENERGY USE WITHOUT IAQ COMPROMISE John Woollett

43 More resources for DCV: Good indoor air quality and low-energy consumption in buildings Mads Mysen Clima 2010, 2013 workshop Chair; John Woollett DCV for better IAQ and energy efficiency Mari-Liis Maripuu

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