This document discusses renewable energy systems for commercial buildings and their control using building automation systems. It provides tutorials on solar hot water and photovoltaic/wind systems. It recommends monitoring renewable energy production with the BAS and controlling solar hot water systems based on temperature differences between the collectors and storage. Case studies demonstrate control sequences for various solar hot water configurations. Key lessons learned are to locate sensors properly and prevent overheating or re-radiation of collected energy.

1. Controlling Renewable Energy
Systems in Commercial
Buildings
Presented to the Illinois Chapter ASHRAE
Tuesday, March 9, 2010
By Gaylen Atkinson
President
Atkinson Electronics

2. 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

3. 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.

4. 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

5. 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

6. 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 DIAGRAM
Warm 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

7. Renewable Energy & Hot Water Control Strategies March 9, 2010
SOLAR THERMAL HOT WATER
DIAGRAM
Cold 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
DIAGRAM
Cold 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
DIAGRAM
Cold climate closed loop drain-back
system – Thermal Example #4
Control Sequences – on next slide

8. 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
DIAGRAM
Multi load solar HW Heating system
Thermal Example #5
Control sequences on next slide
CONTROL SEQUENCES
1. 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.

9. Renewable Energy & Hot Water Control Strategies March 9, 2010
TEST SYSTEM FOR COMPARING
THREE COLLECTOR TYPES
FLAT-PLATES
EVAC-TUBES
DRAIN BACK
OSA PREHEAT BAS MONITORING
Thermal Example #6
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
TYPICAL GRID-TIE PV ARRAY

10. 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

11. 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

12. 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

13. Renewable Energy & Hot Water Control Strategies March 9, 2010

14. 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.

15. 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)

16. 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