controlling renewable energy systems
DESCRIPTION
TRANSCRIPT
Controlling Renewable Energy Systems in Commercial
Buildings
Presented to the Illinois Chapter ASHRAETuesday, March 9, 2010
By Gaylen AtkinsonPresident
Atkinson Electronics
Renewable Energy & Hot Water Control Strategies March 9, 2010
Gaylen Atkinson
Atkinson Electronics, Inc.
Salt Lake City, Utah
MARCH 2010
PRESENTATION OUTLINE
� Tutorial of solar hot water systems and solar facts
� Tutorial of PV & wind renewable energy systems
� BAS renewable energy recommendations
� Control sequences for solar HW systems
� The ASHRAE 2008 summer meeting sustainability
project
� Solar HW system case study: What we learned
� Solar HW system recommendations and conclusions
The sun is the source of all our earth’s energy except
nuclear
It powers:
� Weather
� Daytime heating
� Growing food & plants
� Fossil fuels
� Renewable energy systems
Renewable Energy & Hot Water Control Strategies March 9, 2010
RENEWABLE ENERGY FACTS� Solar – sun shines 8 hours per day on flat surfaces
� Collector height is latitude for annual best efficiency
� PV drops 65-75% with cloud cover. 15% of solar
radiance is maximum collectible
� Solar thermal drops 50-60% with cloud cover. 65% of
solar radiance is maximum collectible.
� Worldwide solar constant used is 1000 W/sq meter or
317 BTU/sq. ft.
� Solar HW system must handle a non-turn-off energy
source
� Wind is site specific – often intermittent.
DECISION ISSUES FOR RE SYSTEMS
IN GREEN BUILDINGS� Project needs LEED points – therefore often minimal
alternatives considered in RE studies.
� RE system added after the fact - without designing it into
the mechanical system from project inception.
� Owner wants RE system and is willing to pay for it for
prestige purposes.
� RE systems designed by engineers with little experience
in RE.
� Proven technologies for RE are practiced outside of our
industry.
TYPES OF RE SYSTEMS IN
GREEN BUILDINGS
�Solar thermal: hot water, pre-heated outdoor air.
�Photovoltaic (PV) electrical power generation.
�Wind turbines.
�Biomass boilers
�Battery storage not typical for green buildings –
used in off-grid applications.
Renewable Energy & Hot Water Control Strategies March 9, 2010
HOW DOES THE BAS SYSTEM FIT
IN?
� Monitoring requirements needed for LEED points.
� Monitoring and operating an RE system is much
different than conventional HVAC.
� BAS for RE requires power plant thought process.
� HVAC BAS is comfort & temperature based.
� Often only a few BAS points need to be added to
accomplish RE energy optimization.
� Custom energy collection programming is often
required as HVAC BAS usually doesn’t include these
algorithms.
MINIMUM REQUIREMENTS FOR
EFFECTIVE RE BAS
�Need enough sensors to permit energy
calculations.
�Need to calculate energy production and log it.
� Instantaneous value, BTU/HR, KW, etc.
�Daily production totals – logged.
�Monthly & seasonal logs for comparison.
�Monitor solar or wind availability if practical.
TWO MAIN TYPES OF SOLAR HW
PANELS
�Flat plates
� Less expensive
� More rugged
� More efficient at lower � T’s to ambient
�Evacuated tubes
� More expensive
� Single glass tubes can be replaced
� More efficient at higher � T to ambient
Renewable Energy & Hot Water Control Strategies March 9, 2010
EVACUATED TUBES & FLAT PLATES
PERFORMANCE GRAPH
EVAC TUBES VS FLAT PLATES
PERFORMANCE GRAPH
EVAC TUBES VS FLAT PLATES
Renewable Energy & Hot Water Control Strategies March 9, 2010
SOLAR HW DESIGN “RULES OF
THUMB”
� Solar water flows for 20° � T in bright sun
� .5 GPM per panel or 25 sq feet
� Increase 20% for glycol
� DOM HW storage of 1 to 2 gallons per sq foot of
collector
� Best payback for 50 to 75% of load for sizing
� Always have coldest water entering collectors
� Put tank stratification to work
� Always incorporate heat rejection
Remember – solar collection efficiency is
inversely proportional to �T to ambient
SOLAR HW DESIGN “RULES OF THUMB”
CONT’
� Design piping for low flow rates, count every elbow and
tee for balance.
� Reduce pressure drop.
� Full port isolation ball values
� Oversize piping
� Use only long radius 90 deg. elbows
� Shorten all runs where possible
� Except for drain-back systems, solar pump must be on
emergency power or use PV powered DC pumping.
Remember! All pumping energy is a parasitic loss, don’t
oversize the pump. Solar compensates.
SOLAR THERMAL HOT WATER DIAGRAMWarm Climate – Thermal Example #1
Control Sequences: If T1 > (T3+10F), TURN ON PUMP If T1 < (T3+1F), TURN OFF PUMP If T1 < T2, TURN OFF PUMP
Renewable Energy & Hot Water Control Strategies March 9, 2010
SOLAR THERMAL HOT WATER
DIAGRAMCold Climate with Glycol – Thermal Example #2
Control Sequences: If (T1 >T3+20F), TURN ON PUMP If T1 < (T3+2F), TURN OFF PUMP If T1 < T2, TURN OFF PUMP
SOLAR THERMAL HOT WATER
DIAGRAMCold Climate w/ Glycol External Heat - Thermal Example #3
Control If T1 > (T3+20F), TURN ON SOLAR PUMP, OFF @ T1 < (T3 + 2F) Sequences: If T2 > (T3+10F), TURN ON DHW PUMP, OFF @ T2 < (T3 + 2F) If T2 > T1, TURN OFF BOTH PUMPS
SOLAR THERMAL HOT WATER
DIAGRAMCold climate closed loop drain-back
system – Thermal Example #4
Control Sequences – on next slide
Renewable Energy & Hot Water Control Strategies March 9, 2010
CONTROL SEQUENCE
1. If T1 > (T3+20F) start solar pump in high speed. Switch
solar pump to low speed after 2 minutes or solar pump � P
or current indicates a closed loop condition.
2. If T1 < (T3+2F), stop solar pump. Interlock DHW pump to
only run when solar pump is running.
3. If T2 > (T3+10F), start DHW pump
4. If T2 < (T3+2F), stop DHW pump (optional)
5. If T2 > T1 stop solar pump
6. If T3 > 180F stop solar pump
7. If T5 (inside tank) > 180F stop solar pump
SOLAR THERMAL HOT WATER
DIAGRAMMulti load solar HW Heating system
Thermal Example #5
Control sequences on next slide
CONTROL SEQUENCES1. Start solar pump from solar radiance signal of about
250 to 300 W/M_, stop pump if T2 > T1.
2. Modulate speed of solar pump with VFD to maintain 20F � T
between T1-T2.
3. If T1 > (T3+20F) and T3 < 120 F set point, start DHW
pump. Stop if T1 < (T3 + 2F).
4. If T4 > (T6 + 10F), modulate valve to maintain T7 set point.
Close valve if T4 < (T6 + 1F).
5. If T5 > (T7 + 20F) start pool HXCR pump. Main pool pump
runs continuously. Stop HXCR pump if T5 < (T7 + 2F).
6. If T2 > 160F set point start DHW pump. Stop DHW pump
when T3 > 180F or T2 < 140F set point.
7. If T2 > (170F set point w/ 20F diff) start pool HXCR pump.
Renewable Energy & Hot Water Control Strategies March 9, 2010
TEST SYSTEM FOR COMPARING
THREE COLLECTOR TYPES
DRAIN BACK
FLAT-PLATES
EVAC-TUBES
OSA PREHEAT BAS MONITORING
� Install flow meter in air handler mixed air section
� Program TM = % OSA x Tosa+ % RTN AIR x Trtn air
� Calculate OSA BTU from (Tosa htd – Tosa) x % OSA x MA flow x
K
Thermal Example #6
TYPICAL GRID-TIE PV ARRAY
Renewable Energy & Hot Water Control Strategies March 9, 2010
PV GRID-TIE POWER SYSTEM
� Need good solar availability.
� Net metering with utility, inverter shuts off when utility is down.
� Utility power grid is storage reservoir
TYPICAL GRID-TIE INVERTERS
3 _ 208V GRID-TIE PV SOLAR WIRING
DIAGRAM
Renewable Energy & Hot Water Control Strategies March 9, 2010
PV POWER GENERATION
DATA PROVIDED BY INVERTER
� Instantaneous AC KW, array voltage.
� KW/HR, KW/day, total KW, faults.
� Some have input power & inverter efficiency.
� BAS needs to merely display & log inverter data.
� Most inverter manufacturers provide protocols for
data collection.
PV OPERATING CAUTIONS
� Have clean panels and avoid shadowing at
anytime.
� Verify site to not have shadows from poles etc.
� Monitor daily, monthly energy production to catch
problems before lost opportunities continue.
� Net-metering utility payback may only be avoided
generating cost. Maximize gain by matching
electrical load with PV energy production.
� Remove snow promptly in cold climates to not lose
collection days.
BUILDING-SIZE WIND TURBINE
Renewable Energy & Hot Water Control Strategies March 9, 2010
WIND GRID-TIE POWER SYSTEM
� Need good wind availability.
� Net metering with utility, inverter shuts off when utility is down.
� Utility power grid is storage reservoir
Renewable Energy & Hot Water Control Strategies March 9, 2010
Renewable Energy & Hot Water Control Strategies March 9, 2010
UTAH ASHRAE SOLAR
PROJECT
Live data web site
www.utahashraesolar.tzo.co
m
Use it for:
�BAS monitoring example for RE systems
�Energy calculation example for RE systems
�RE energy performance example in cold climate
SOLAR HOT WATER BAS
MONITORING
� Need temp sensors on all collector, tank and heat
exchanger input & output lines.
� Measure flow with a 1 pulse per gallon flow meter or
virtual flow from constant speed pump curve.
� Calculate BTUS from 1 pulse x temp DT and totalize.
� Adjust flow calculation for glycol, specific heat etc.
� Log all temp sensors, flows & calculated BTU’s.
� Use PV powered DC pumping for variable speed
load matching between availability and collection.
THINGS WE LEARNED OPERATING
THE ASHRAE SOLAR HW SYSTEM� Found re-radiation of collected energy, thermo-syphon
& unnecessary pump operation.
� Found owner supplied usage estimates way too high
on weekends, had excessive overheating in summer.
� Added overheating heat rejection valve for safety.
� Had to fix existing thermal mixing valve.
� Added tank transfer pump to maximize HW storage.
� Added glycol for winter operation, needed larger pump.
Renewable Energy & Hot Water Control Strategies March 9, 2010
GENERAL SOLAR HOT WATER
CONTROL
� Imperative to locate collector sensors on both outlet
& inlet, not inside building.
� Start & stop pump from collector outlet temperature
compared against storage tank temperature.
� Stop pump when collector outlet temp is less than
collector inlet to prevent re-radiation.
� Prevent collector over-heating with light loading by
having a means of heat rejection.
SOLAR HOT WATER CONTROL
CONT’D
� Consider tank transfer capability to optimize solar
collection and minimize heat rejection.
� Avoid storage tank losses by matching usage to time
of day when hot water is collected.
� Incorporate freeze protection features such as
draindown or running pump in non-glycol systems.
� Incorporate re–radiate at night features for long
period low loads. (Vacation mode)
Renewable Energy & Hot Water Control Strategies March 9, 2010
CONCLUSIONS
� RE systems are here to stay in green buildings
� RE systems require power generation thinking
� BAS systems can enhance RE renewable energy
output efficiency by calculating & logging energy
data and monitoring system energy production
� Maintenance staff needs to clean collectors
regularly, dirt can drop both PV and thermal
efficiency by 25%
� Live RE system graphics on BAS facilitate operation
& user understanding