1. HCB 3-Chap 20B: Air- Water_Hybrid 1 Chapter 20 B: AIR-WATER AND HYBRID SYSTEMS Agami Reddy (July 2016) Description of traditional air-water system configurations - 2-pipe and 4-pipe - central air for ventilation Chilled beams (active and passive) Dedicated Outdoor Air System ( DOAS) - principle and advantages - different components Evaporative cooling: direct and indirect Desiccant dehumidification systems Variable refrigerant flow (VRF) systems

2. HCB 3-Chap 20B: Air- Water_Hybrid 2 Fig. 20.1 Photo of a room with trickle ventilation along with baseboard heating (from Kolderup)

3. HCB 3-Chap 20B: Air- Water_Hybrid 3 Fig. 20.2(a) Two-pipe air-water system with local outside air supply and fan coil terminal units. A single circulation pump is used. Outdoor air can be supplied locally (by unit ventilators) or centrally via a constant-volume system. Traditional Air-Water Systems

4. HCB 3-Chap 20B: Air- Water_Hybrid 4 Fig. 20.3 Cross-sectional diagram of four-pipe fan coil unit showing outside air supply and two separate coils.

5. HCB 3-Chap 20B: Air- Water_Hybrid 5 Central Air-Water System: -A larger volume of room air than the fresh air inflow is drawn thru the terminal units and is either heated or cooled by secondary water piped from the boiler room or the chilled water plant. -Ventilation air is about 15-25% of the total airflow thru outlet -Typical applications: Exterior spaces of office buildings not requiring close control of humidity Primary or ventilation air (usually constant) Fig. 20.4 Central closed loop individual water heat pump units with a central ventilation system

6. HCB 3-Chap 20B: Air- Water_Hybrid 6 Can also use individual heat pumps But there needs to be a separate outdoor air supply with its own conditioning systems Boilers – Comes on when loop temperature < 70 F - Heat pumps do not supply any heat - All heating supplied by boiler Cooling tower- cools down loop water by evaporative cooling Comes on when loop temperature > 90 F - Heat pumps still supply cooling

7. HCB 3-Chap 20B: Air- Water_Hybrid 7 Outdoor air brought in to meet ventilation needs- This air needs to be conditioned- Requires its own heating and cooling equipment Plan view Inside the rooms

8. HCB 3-Chap 20B: Air- Water_Hybrid 8 AdvantagesDisadvantages Ideally, combines the best features of all-water and all-air systems If designed badly, the worst features of all- water and air-systems can result Low transport energy needed while meeting ventilation comfort requirements Requires more maintenance because of numerous individual zone units Air duct size reducedControls tend to be more complicated Central air handler size reducedNot suitable for high exhaust air requirements Good for spaces with highly variable loadsSevere damage if pipes leak Easy to shut off water supply in unoccupied spaces Cannot shut off primary air to unoccupied spaces Good for exterior spacesHumidity control may be difficult Can simul. heat and cool different spaces Can be combined with ventilation heat recovery devices (heat wheels) Can be combined with water loop HP Table 20.1 Advantages and Disadvantages of Air-Water Systems

9. HCB 3-Chap 20B: Air- Water_Hybrid 9 Chilled Beams (can get 4-14 LEED points) Chilled Beams are coils meant to provide Space sensible cooling- by passing chilled water thru them Cannot provide dehumidification! Heat transfer by both convection (primary mode) and radiation Primarily used for cooling Much higher cooling capacity (4 – 6 times greater) than radiant systems Elevated temperature ( around 60 o F) chilled water used (to avoid condensation in the space) Chilled beams can provide better thermal comfort and lower energy cost than traditional HVAC systems Typical applications: offices and admin areas Chilled beams can be a cost effective solution for laboratories. Low noise, significant energy savings, good occupant comfort!

10. HCB 3-Chap 20B: Air- Water_Hybrid 10 Passive Chilled Beams There are two types of chilled beams: - Passive and Active Passive Chilled beams providing the cooling effect by natural convection and flow of the room air thru the cooling coil. Chilled water circulates inside the chilled ceiling cooling coil. piping. There is no primary air supply. Fig. 20.23 Ceiling mounted passive chilled beam (a) Picture of a unit, (b) Air flow patterns with interior components

11. 11 Max about 400 Btu/hr-ft Fig. 20.25 Example of a specification sheet of a passive chilled beam manufacturer f o free area of bottom perforated cover plate (%), B width (mm), H height (mm) and Z suspension height from lower edge of ceiling to upper edge of chilled beam (mm) HCB 3-Chap 20B: Air- Water_Hybrid

12. 12

13. HCB 3-Chap 20B: Air- Water_Hybrid 13

14. HCB 3-Chap 20B: Air- Water_Hybrid 14 Active Chilled Beams Active Chilled beams (also called Induction Chilled Beams) provide cooling effect by integrating primary air supply induction effect and supplementary cooling by a built in cooling coil. Chilled water circulates inside chilled ceiling cooling coil piping. An air system supplies primary air @ around 60 o F for ventilation and space dehumidification to the Ceiling Induction Diffuser. The ratio between primary air and total supply air can vary from 1:5 to 1:3 The separate air system can be a DOAS with dehumidification capability

15. HCB 3-Chap 20B: Air- Water_Hybrid 15 Active or Induction Chilled Beams (have conditioned primary air supply ) Max about 600 Btu/hr-ft Fig. 20.24 Ceiling mounted active chilled beams (a) Picture of a unit, (b) Air flow patterns with interior components

16. HCB 3-Chap 20B: Air- Water_Hybrid 16 Hybrid Systems with Chilled Beams Separate air system is required for ventilation (outdoor air) and space dehumidification. The separate air system can be a DOAS with dehumidification capability, Often chilled beams because of their limited cooling capacity are used in conjunction with CAV systems (only recently are they being used with VAV systems) They are also used with underfloor and displacement ventilation Underfloor Displacement ventilation

17. HCB 3-Chap 20B: Air- Water_Hybrid 17 Dedicated Outdoor Air Systems(DOAS) Single Zone Systems are simple as far as introducing the proper amounts of Outdoor Air (OA) Multiple – Zone Recirculation Systems (typically VAV) are problematic since it is difficult to guarantee the proper amounts of OA during entire range of climatic conditions 100 % Outdoor Air Systems (or DOAS) are the most reliable system for introduction proper amounts of OA for multiple zones during the full operating range of the system.

18. 18 The term DOAS is used differently by different people. -To some DOAS is the outdoor air conditioning unit (as shown above) which also meets the room latent load, -To others, for a system to qualify as DOAS it needs to satisfy the above condition PLUS (a) outdoor air and return air are totally separated, (b) return air is not recirculated, (c) exhaust air heat recovery HX used, (d) efficient room air distribution sensible devices used (chilled beams, radiant panels,…)

19. HCB 3-Chap 20B: Air- Water_Hybrid 19 DOAS contd… DOAS units are 100 % Outdoor Air units with the ability to bring 100 % outdoor air to all spaces at all times Typical DOAS are air-handling units that cool, dehumidify, heat, humidify and filter the outdoor air prior to being introduced to the conditioned space This approach allows the individual space units to handle only the space cooling and heating loads. It is preferable, however, to introduce the outdoor air at lower humidity ratio than the desired space humidity ratio in order to allow the zone HVAC unit to handle only the space sensible cooling load. Must have a heat recovery system Significant energy savings are said to occur since generally 20-30% less outdoor air must be conditioned as compared to a VAV system for multizone spaces

20. 20 Components of DOAS unit: 1-2 Air cooled and dehumidified by enthalpy wheel (max effective. about 85%) 2-3 Supply air passes over a dehumidification coil to cool as necessary but more importantly to dehumidify the air to a state which can meet the latent loads of the space as well. In case the outdoor air is dry enough, the cooling coil need not dehumidify the air. Advised not to use DX coil, but a chilled water coil because of additional control 3-4 Another sensible heat wheel is used to heat the supply air as necessary Fig 20.26 General arrangement of the DOAS with state points

21. Example 20.6 DOAS Design Example HCB 3-Chap 20B: Air- Water_Hybrid 21

22. HCB 3-Chap 20B: Air- Water_Hybrid 22

23. HCB 3-Chap 20B: Air- Water_Hybrid 23 4

24. HCB 3-Chap 20B: Air- Water_Hybrid 24 C OMMENTS In addition to the DOAS cooling coil, the designer has to select a sensible cooling system to remove the sensible loads of the space. Several options are available: chilled beams or radiant cooling panels or DX systems such as mini split units (VRF), or chilled water based fan coils units.

25. HCB 3-Chap 20B: Air- Water_Hybrid 25 Typical DOAS include the following major components:

26. HCB 3-Chap 20B: Air- Water_Hybrid 26 Typical Application of DOAS unit ( schools), from 2007 ASHRAE Handbook, chapter 6 : combined with Displacement Ventilation – - - One could also use Chilled beams or Radiant sails Fig. 20.28 DOAS with parallel radiant cooling system

27. HCB 3-Chap 20B: Air- Water_Hybrid 27 Fig. 20.29 Simple payback estimates of promising HVAC technologies (Redrawn from U.S. DOE, 2002)

28. HCB 3-Chap 20B: Air- Water_Hybrid 28 Evaporative Cooling Evaporative cooling systems have been utilized for many years for applications such as residential, commercial, and industrial. They are cost effective in low wet bulb locations. The process of evaporative cooling is an adiabatic evaporation of water which provides the cooling effect. Three(3) evaporative cooling mechanisms are typically used: - Direct Evaporative Cooling - Indirect Evaporative cooling. - Indirect/Direct Evaporative Cooling In many cases indirect evaporative cooling systems used to pre-cool the air and additional mechanical cooling maintains desired conditions. Special attention is given to water treatment issues.

29. HCB 3-Chap 20B: Air- Water_Hybrid 29 Fig. 20.30 (a) Direct evaporative cooler showing key components, including wetted pads, blower, motor, and water supply system. (b) Typical direct evaporative cooling process plotted on the psychrometric chart

30. HCB 3-Chap 20B: Air- Water_Hybrid 30 Evaporative Cooling This is an incomplete adiabatic saturation process Model using concept of “available DBT depression %” Say, if this is 80%, then 110-0.8x(110-75.5)= 82.4 is the exit DBT of air 3

31. HCB 3-Chap 20B: Air- Water_Hybrid 31 Fig. 20.31 Evaporative cooling media Fig. 20.32 Example of evaporative cooler effectiveness fFor different pad thickness and air flows

32. HCB 3-Chap 20B: Air- Water_Hybrid 32 Fig. 20.33 Map of lines of constant Summer WBT in the US At the 5% frequency level

33. HCB 3-Chap 20B: Air- Water_Hybrid 33 : Fig. 20.35 Indirect and direct evaporative cooling processes plotted on a psychrometric chart. Indirect process is at constant humidity ratio whereas direct process is at constant enthalpy Psychrometrics of Evaporative cooling systems

34. HCB 3-Chap 20B: Air- Water_Hybrid 34 Direct- Indirect Evaporative Cooling Fig. 20.34 Indirect evaporative cooler system diagram.

35. HCB 3-Chap 20B: Air- Water_Hybrid 35 Active Desiccant Based Dehumidification Systems Fig. 20.40 Active desiccant based dehumidification system (Courtesy of Munters, DryCool)

36. HCB 3-Chap 20B: Air- Water_Hybrid 36 Active Desiccant Systems contd… Desiccant dehumidifier attracts moisture from the air thru a difference in vapor pressure. As the air dehumidifies in the desiccant its latent heat is converted to sensible heat resulting in increase of the air temperature. Every desiccant unit has two air streams. Process air and Reactivation air (sometimes called Regeneration) Thermal energy used to reactivate the desiccant Desiccant materials naturally attract moisture from gases and liquids.

37. HCB 3-Chap 20B: Air- Water_Hybrid 37 Active Desiccant Systems contd… The material becomes saturated as moisture is absorbed or collects on the surface; but when heated, the desiccant dries out (regenerates) and can be used again. Conventional solid desiccants include silica gel, activated alumina, molecular sieves. Titanium silicate, a class of material called "1M," and synthetic polymers are new solid desiccant materials designed to be more effective for cooling applications. The desiccant is impregnated or formed in place in an Honeycomb Matrix.

38. HCB 3-Chap 20B: Air- Water_Hybrid 38 Fig. 20.39 Desiccant and regeneration system with process (space supply) and return air streams.

39. HCB 3-Chap 20B: Air- Water_Hybrid 39 Fig. 20.41 More common practical system Often system is made up of separate return air stream and regeneration air stream

40. HCB 3-Chap 20B: Air- Water_Hybrid 40 Active Desiccant Systems contd… Typical applications are: - DOAS for hotels, schools, dormitories - Dehumidification in Supermarkets, Ice Rinks, & industrial facilities where the desired humidity level is lower then typically achieved by mechanical cooling (Mechanical cooling can provide around 50 Grains/lb or 0.0007 lb/lb)

41. HCB 3-Chap 20B: Air- Water_Hybrid 41 Variable Refrigerant Flow (VRF) Systems

42. HCB 3-Chap 20B: Air- Water_Hybrid 42 Invented in Japan by Daikin VRFs use refrigerant as the cooling and heating medium. Conditioning of the refrigerant by a single outdoor condensing unit, and is circulated within the building to multiple fan coil units. Good application in add-ons, historical buildings, retrofit situations, office buildings, strip malls, banks, schools, hotels, etc due to compartmentalized comfort conditioning. VRF systems are enhanced versions of ductless multi-split systems, permitting more indoor units to be connected to each outdoor unit and providing additional features such as simultaneous heating and cooling and heat recovery. VRF technology uses smart integrated controls, variable speed drives, refrigerant piping, and heat recovery to provide products with attributes that include high energy efficiency, flexible operation, ease of installation, low noise, zone control, and comfort using all-electric technology. Introduction to VRF

43. HCB 3-Chap 20B: Air- Water_Hybrid 43 Provides individualized air conditioning to different rooms as needed

44. HCB 3-Chap 20B: Air- Water_Hybrid 44 VRF HVAC systems are DX heat pump technology platform built on standard reverse Rankine vapor compression cycle. Salient Features of a VRF system: a) Zoning System. b) Operates as Heat Pump. c) Simultaneous heating and cooling. d) Multiple indoor units- Up to 50 indoor units per system. e) Connected Diversity- Up to 150%. f) EMS/BMS Compatibility. g) Inverter Technology/ Variable speed compressor. System Types : There are 3 basic types of VRF systems 1) Cooling only. 2) Heat Pump 3) Heat Recovery

45. HCB 3-Chap 20B: Air- Water_Hybrid 45 Installation Advantages: Lightweight and modular. Modularity enables staged or floor by floor installation. Easy retrofitting. Comfort: Many zones possible each with individual set point control. Capacity Modulation: VRF systems enable wide capacity modulation and bring rooms to the desired temperature extremely quickly and keep temperature fluctuations to minimum. Precise temperature control. Energy efficient: Ductless system, therefore no losses. Simultaneous heating and cooling to different zones are possible, each individual indoor unit can be controlled by a programmable thermostat. Separate billings can be generated by VRF systems which makes individualizes billings easier. Variable speed compressors with 10 to 100% capacity range can be used by VRF systems that provide unmatchable flexibility for zoning to save energy. Advantages of VRF Systems

46. HCB 3-Chap 20B: Air- Water_Hybrid 46 Outcomes -Knowledge of the different types of traditional air-water systems and how they differ from all-water and all-air systems -Understanding the operational principles of the traditional air-water system types -Understanding the advantages and disadvantages of air-water systems -Knowledge of the two different types of chilled beams and their operational principles -Be able to design chilled beams for rooms given manufacturer’s tables -Understanding the unique features of DOAS and the dvnatges they provide -Be able to design DOAS systems for simple cases -Knowledge of different types of evaporative cooling systems and understanding their operating principle -Knowledge of active desiccant system configurations, and understanding their operating principles -Familiarity with VRF systems and their advantages