Controlling renewable energy systems

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 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.


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


EVACUATED TUBES & FLAT PLATES

PERFORMANCE GRAPH

EVAC TUBES VS FLAT PLATES

PERFORMANCE GRAPH

EVAC TUBES VS FLAT PLATES


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


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


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


DIAGRAMCold climate closed loop drain-back

system – Thermal Example #4

Control Sequences – on next slide


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


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.


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


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


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


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


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.


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)


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

Controlling renewable energy systems

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