Building Energy Systems. - HVAC: Heating, Distribution -

Transcription

1 * Some of the images used in these slides are taken from the internet for instructional purposes only Building Energy Systems - HVAC: Heating, Distribution - Bryan Eisenhower Associate Director Center for Energy Efficient Design Researcher and Lecturer Department of Mechanical Engineering UCSB Winter 2015

2 HVAC Cooling: (Natural Ventilation) Refrigeration cycles Absorption cycles Evaporation Heating: (Natural through envelope solar, internal gains) Boilers (water / steam) Furnaces Electric Refrigeration Natural solar collector ** These subjects cover how to create cooling/heating, distribution comes later

3 Boilers Exchanges heat from combusted fuel (oil, gas, wood, coal, elec., etc.) with water If water boils steam If water does not boil hot water (still called a boiler) A specification of the boiler is its steam pressure A boiler needs combustion air but this air does not circulate through the building, water or steam is sent to the building The capacity of the boiler signifies how much heat it can produce The efficiency of the boiler depends on how much load is on the boiler, the part load ratio (0-1) defines whether the boiler is off or at full capacity The hot water or steam is taken to the building and exchanged with the zone Steam systems are typically more expensive to install because they work at higher pressures Water systems have less losses because their temperatures are lower

4 Furnaces Air is forced over a combustion chamber or electric heater The burners operate on different combustibles (e.g. oil, gas) Return: Cool air is taken from the zones/house (through a filter) and mixed with fresh outdoor air Supply: Warm air is distributed throughout the building Combustion exhaust goes up through the roof Heat exchanger design and variable fan speed influence system efficiencies Condensing furnace: High efficiency furnaces extract so much heat from the air that water vapor condenses utilizing the latent heat

5 Electric heating The combustion processes can be replaced with electric elements (much like inside an electric oven) Benefits are cheaper equipment, good efficiency for all loads, no exhaust Disadvantage: electricity costs usually much more than gas costs Remember that electricity needs to be created at a plant (using gas, oil, coal) and then transported to your building Generation and transmission losses make electric heating less desired On-site renewable electric generation could change this (wind, solar, )

6 Electric vs. Gas Gas ~ 90% efficient, cleaner than coal Electric ~ 25% efficient, higher emissions due to coal burning

7 Service water The hot water generated from the boiler is not suited for human consumption Different standards are made for heat exchangers that are used for drinking etc. Hot service water is sometimes included in described HVAC equipment These hot water heaters are similar to what you have in your house, with a few other variations possible

8 Solar Collectors Plenty of free heat can be gained through absorption in the envelope or through windows Solar thermal collectors are devices that collect solar heat and bring it into the building through HVAC equipment Just like regular windows, a solar panel collector has optical properties that limit the amount of heat gained Additionally, since a hot liquid (often water) is running through tubes on the roof, heat transfer occurs between the tubes and ambient, reducing the efficiency as this temperature difference increases SDH

9 Solar Collectors Flat plate Contains about 40 gallons of water about enough for one persons residential needs Evacuated tube More efficient at higher temperature differentials (e.g. very cold out) Parabolic Often need to angled directly at sun, don t pick up diffuse radiation Evacuated tube Flat plate collector wikipedia solartribune.com

10 HVAC Occupied area Earth Past Air Distribution Now Secondary Systems Past Primary Systems EnergyPlus documentation

11 Distribution Units (water) Cooling / Heating can also be brought into the building directly, without the air flow Different methods: High temperature steam Mid temperature hydronic (floor, baseboard) High temperature electric Quiet, no particulates, heat usually touches body directly (e.g. feet) Don t get fresh air Up to 50% of the heat transfer is actually convection Steam Radiator Radiant cooling Underfloor heating Hydronic Radiator

12 Distribution Units (water) Fan coil units: Fan and heating/cooling coil (heat exchanger) in one unit Installed in occupied space which means no ducting needed Economical install but fan noise may be a problem fanupdate.blogspot.com Thermal Storage: Can store cooling in thermal mass of the building or in chilled water / ice Can store up to a million pounds of ice that is created at night, used during the day Optimization possibilities are when to make the stored energy and how much

13 Single Duct Reheat Preheating/cooling at the AHU is performed to maintain the coldest supply temperature for the entire building Zones that don t need this cold air will reheat it Optimization potential: what is the coldest air that is necessary? Chilled water loop Exhaust Return Air Reheat Outdoor Air Air Handling Unit (AHU) Supply Air Economizer Fan Filter Cooling / Heating Coils Preheat / Precool Hot water loop

14 Distribution Units (Air) The cooling needs of each zone in a building may be different (e.g. the computer lab vs. the library vs. the kitchen) Single duct systems: The cooling of the air in the AHU may be just enough for some zones but too much for others. To account for this, the air is cooled enough for all zones and reheated for the zones that don t need that much cooling Dual duct systems Dual duct systems combine just enough cold and hot air to maintain comfort in each zone Note there are many smaller variations including fans/dampers in the terminal boxes, electric reheat, etc. Single duct VAV reheat Hot water Dual duct mixing box

15 Single Duct Reheat Preheating/cooling at the AHU is performed to maintain the coldest supply temperature for the entire building Zones that don t need this cold air will reheat it Optimization potential: what is the coldest air that is necessary? Chilled water loop Exhaust Return Air Reheat Outdoor Air Air Handling Unit (AHU) Supply Air Economizer Fan Filter Cooling / Heating Coils Preheat / Precool Hot water loop

16 Single Duct Reheat Variants: Direct expansion for the AHU, electric preheat or reheat, some combination of the all? Exhaust Return Air Electric Reheat Outdoor Air Air Handling Unit (AHU) Supply Air Economizer Fan Filter Cooling / Heating Coils Direct expansion Preheat / Precool

17 Dual Duct Preheating/cooling at the AHU is performed to generate two supply temperatures Each zone mixes these flows as needed Optimization potential: what are the two temperatures of the supply ducts? Chilled water loop Exhaust Return Air Outdoor Air Air Handling Unit (AHU) Mixing Box / / / / Hot Deck Supply Air Cold Deck Economizer Fan Filter Cooling / Heating Coils Preheat / Precool / / / / Hot water loop

18 Summary of a few different types of Heating and cooling layouts There are a large number of possibilities to cool/heat a building given all the different components available.

19 Chillers Air Air Air Air Typical chiller configurations Pictured is a vapor compression chiller, the diagram is similar for absorption chillers Air-cooled Heat to Atmosphere Liquid Liquid-cooled Evaporative Cooling Tower Heat to Atmosphere Refrigerant Condenser Refrigerant Condenser Expansion Compressor Expansion Compressor Liquid Evaporator Energy added Liquid Evaporator Energy added Radiant panel, AHU cooling coil, fan coil unit Radiant panel, AHU cooling coil, fan coil unit Heat from building Heat from building

20 Heat Pumps (cooling) Air Air Air Air Heat pumps can be configured in many ways Two ways are shown below, but these can be partially interchanged (e.g. airto-liquid) Liquid Liquid-to-Liquid Ground, lake, etc. Heat to Earth Air-to-air Refrigerant Condenser Heat to Atmosphere Expansion Compressor Refrigerant Condenser Expansion Compressor Liquid Evaporator Energy added Evaporator Energy added Radiant panel, AHU cooling coil, fan coil unit Heat from building Heat from building

21 Heat Pumps (heating) Heat pumps can be configured in many ways Two ways are shown below, but these can be partially interchanged (e.g. airto-liquid) Liquid Liquid-to-Liquid Ground, lake, etc. Heat from Earth Air-to-air Refrigerant Condenser Heat from Atmosphere Expansion Compressor Refrigerant Condenser Expansion Compressor Liquid Evaporator Energy added Evaporator Heat to building Energy added Radiant panel, AHU heating coil, fan coil unit Heat to building

22 Heating Boiler Liquid, steam Furnace Radiator, AHU heating coil, fan coil unit Air Heat to building Air Heat to building

23 Implementing in OS Two high level approaches to Heating and Cooling implementation 1) Ideal air loads: Systems and plant is not modeled, cooling and heating come from the district 2) System and plant modeling: many different choices to implement different system components and plant Ideal Loads System Modelling

24 Open Studio HVAC systems The online tutorial is a very addendum to this lecture:

25 Terminal units only Open Studio HVAC systems Two main ways to implement HVAC Terminal units only (e.g. no plant, just energy that is needed in the zone) Entire plant and terminal units Outdoors Fresh Air Hot Water Chilled water Refrigerant Cooling Tower Controllers Thermal Zone

26 Terminal Units Only For each zone, select Ideal loads off, drag the PTHP from the library to the HVAC system Thermostat on, drag clgstp, htgstp to the cooling and heating thermostat schedules Do this for all 5 zones

27 Open Studio HVAC systems Detailed system w/plant: To insert a new HVAC system, go to the HVAC tab on the left and push the green + symbol to add a system.

28 Air Loop The General Idea: Unoccupied area (roof, basement, outside) Inside You can add zones here, this wont be done on all slides but it is implied.

29 Plant Loop The General Idea: When you add air loop components that need a plant, OpenStudio will add a plant loop as necessary

30 Open Studio HVAC Templates Packaged rooftop unit Fresh air intake and exhaust DX Direct expansion cooling (no water involved, expansion of refrigerant cools air) Gas fired heat Constant speed fan

31 Open Studio HVAC Templates Packaged rooftop heatpump Heat pump provides heating or cooling. Supply air fan built into this sub-model

32 Open Studio HVAC Templates Packaged DX rooftop VAV with reheat Cooling is same as Packaged rooftop unit. Initial heating provided from either steam or hot water from plant Variable speed fan Reheat is from plant Damper controls flowrate

33 Open Studio HVAC Templates Packaged Rooftop VAV with Parallel Fan Power Boxes and Reheat Cooling and heating same as Packaged rooftop unit Variable speed fan Reheat is from plant Damper, fan controls flowrate

34 Open Studio HVAC Templates Packaged Rooftop VAV with Reheat Cooling and heating both from plant Varibable speed fan Reheat is from plant Damper controls flowrate

35 Open Studio HVAC Templates VAV with Parallel Fan-Powered Boxes and Reheat Variable speed fan

36 Open Studio HVAC Templates Warm Air Furnace Gas Fired Warm Air Furnace Electric Heat with either a gas or electric furnace Constant speed fan

37 UCSB Buildings A number of mechanical schedules have been uploaded to the website. You will need to implement the Air Handling Units only, using VAV reheat Adding fan coil units and other heating/cooling devices is optional and/or may be requested for the final.