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Climate Control Training
21/09/2016
2016 FEC Energy
© 2016 FEC Energy
Heating, ventilation & screen gapping Translating the theory into practice
© 2016 FEC Energy
Ventilation – lee side vs. wind side
Wind
side
Lee side
Wind
© 2016 FEC Energy
Vent position and air exchange
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Vent position %
Re
lati
ve
air
ex
ch
an
ge
Lee side Wind side Both
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
Vent position (%)
5% vent = 20% of air exchange
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Climate Control Training
21/09/2016
2016 FEC Energy
© 2016 FEC Energy
Venting The set points we have to work with:
• Lee side
• Vent temperature
• Minimum vent position
• Wind side
• Vent temperature & minimum vent position
• Influences
• Humidity
• Radiation
• Outside temperature
• Wind speed
© 2016 FEC Energy
Heat / vent strategy – a possible approach
• Note
• Always look at calculated heat & vent temperatures
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Time
oC
Heating temperature Ventilation temperature
© 2016 FEC Energy
Heat / vent strategy – smoother transitions
• Note
• Apply radiation influences to both heat & vent
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oC
Heating temperature Ventilation temperature
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Climate Control Training
21/09/2016
2016 FEC Energy
© 2016 FEC Energy
Heat & vent strategy – points to consider • Looking for
• Parallel lines
• Apply all light influences equally to heat & vent strategies
• Slow ramp up & down of temperatures – including the effect of influences (if possible)
• Constant difference between the heat & vent temperature • Applying any humidity influences will be much easier
© 2016 FEC Energy
Basic heat-vent temperature differentials
• Heating & control system should be able to achieve target temperature +/- 0.5°C, if not better
• Lee side vent temperature = heat + 1°C
• Wind side (winter setting) = heat + 3°C (at least)
• Wind side (summer setting) = heat + 2°C (reducing to 1°C at low wind speed)
• Note: • This relates to ‘warm crops’ (20°C)
• It’s all about temperature difference, inside - outside
© 2016 FEC Energy
• How to set a heat / vent strategy
Heat / vent strategy
Time the change starts
Automatic sunrise / sunset adjustment
Ramp up time
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Climate Control Training
21/09/2016
2016 FEC Energy
© 2016 FEC Energy
• How to set a heat / vent strategy
Heat / vent strategy
© 2016 FEC Energy
Go to a greenhouse
© 2016 FEC Energy
Skip to humidity definitions & units
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Climate Control Training
21/09/2016
2016 FEC Energy
© 2016 FEC Energy
Before we go any further…
• Whatever humidity measurement you use
• RH, HD or VPD
• Wherever you measure humidity
Makes no difference to the principles discussed in this session
© 2016 FEC Energy
Scenario • Day RH
• <85% I’m happy
• >90% sweaty palms & all influences to the maximum
• Night RH • <90% I’m happy
• >95% sweaty palms & all influences to the maximum
© 2016 FEC Energy
What is an ‘Influence’ • Change in a set point driving by a secondary variable
• For example: • Set point might be
• Heat/vent temp, min pipe, min vent
• Influence might be
• Light level, humidity, outside temp, wind
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Climate Control Training
21/09/2016
2016 FEC Energy
© 2016 FEC Energy
• Beware of rapidly-changing influences
– This includes radiation as well as humidity
Influences
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Time
RH
%
© 2016 FEC Energy
• Influences on vent temperature
– Some computers use the actual measured value
– Some use deviation from a target value – e.g. 85 %
Vent temperature
RH oC
80 0
85 -0.5
90 -0.8
95 -1
RH oC
-5 0
0 -0.5
+5 -0.8
+10 -1
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RH %
oC
Heat Vent
© 2016 FEC Energy
‘But humidity control using influences on vent temperature gives erratic vent movement and causes dips in temperature’
SOLUTION
• Apply small influences over as big a humidity range as possible
• Use an appropriate P-band
• Proportional band
• The amount of venting is in proportion to how much the measured temperature is above the ventilation temperature
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Climate Control Training
21/09/2016
2016 FEC Energy
© 2016 FEC Energy
P-bands – how they work
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delta T (above ventilation temperature)
Ven
t p
osit
ion
P-band = 3 P-band = 10
© 2016 FEC Energy
P-bands • Say you are venting at 25°C
• P-band = 20°C
• You only get 100% vent at a greenhouse temperature of 45°C!!!
• Some people find this thought quite scary
• Outside temperature influence on P-band
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Outside temperature oC
P-b
an
d o
C
© 2016 FEC Energy
Minimum vent Minimum vent is the amount of ventilation you get
irrespective of greenhouse temperature
• Some growers use it like minimum pipe • It’s now March – ‘Just a couple of %, that’s all’
• Note • 5% lee side vent can give as much as 20% of the air exchange that
100% vent gives
• There is a place for minimum vent • But you need to be aware of its limitations
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Climate Control Training
21/09/2016
2016 FEC Energy
© 2016 FEC Energy
• Don’t get carried away – particularly in the shoulder seasons – A fixed minimum vent might work fine one night if it’s mild
– But a cold snap would mean it’s unnecessary
Minimum vent
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oC
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Vent Vent Measured Min vent RHHeat
© 2016 FEC Energy
• Influences on minimum vent
Minimum vent
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RH%
%
© 2016 FEC Energy
Start End
Basic minimum vent 85 90 3
Outside temperature 10 5 -2
Deviation heating temperature 0 -1 -3
Wind speed 2 6 -1
RangeValue
• Influences on minimum vent • Fine tuning minimum vent – why was it ‘spot on’
yesterday, but not today? • It is colder / warmer outside
• It is windy
• Different light levels
• Depending on the influences available you could end up with something like this:
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Climate Control Training
21/09/2016
2016 FEC Energy
© 2016 FEC Energy
Minimum pipe temperature – definition
The pipe temperature is kept at this level even when there is no demand for heat to maintain the
greenhouse temperature.
© 2016 FEC Energy
• Minimum pipe temperature • Why do we use it?
• Air movement
• 15°C above greenhouse temperature = reasonable air movement
• More than 20°C higher = little point for extra air movement
• The reason >20°C works well in practice is it usually makes the vents open
• So why not open the vents in the first place?
• Why not turn it off completely when
• The vents are open
• The greenhouse temperatures & humidity are fine
© 2016 FEC Energy
• Heating temperature = 20 °C
• Pump on = 30 °C, pump off = 25 °C
• Basic minimum pipe of 30 °C
Minimum pipe
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RH %
oC
Calc MP Basic MP
RH oC
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85 +5
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Climate Control Training
21/09/2016
2016 FEC Energy
© 2016 FEC Energy
Minimum pipe temperature – radiation influences
Radiation influences – ‘high’ light levels mean • Warm plant
• Good humidity
• Vents will be open
• Low minimum pipe temperature required
Judging the right light levels to use • High light + warm day = vents open + good humidity
• High light + colder day = vents open? good humidity?
• Maybe not
© 2016 FEC Energy
Minimum pipe temperature – the alternative to
radiation influences
• Humidity influences • To reduce minimum pipe
• High light + warm day • Humidity will be good, vents will be open
• Minimum pipe will be reduced
• High light + cold day • If humidity is good, minimum pipe will reduce
• If humidity is poor, minimum pipe will stay on
• Low light + very cold day • Humidity will be very good = minimum pipe very low?
© 2016 FEC Energy
Some problems
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oC
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oC
Heat Vent Air temperature HD(x10) Meas pipe Meas lee
Unstable pipe temperature Unstable air temperature
Cyclical venting Oops
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Climate Control Training
21/09/2016
2016 FEC Energy
© 2016 FEC Energy
The answers • Venting
• Reduce the vent temperature using humidity influences to open the vents sooner, and help control the rate of rise of temperature
• Avoid ‘over-venting’ by increasing P-bands with low outside temperature
• Take the bottom out of cyclic vent movement, using minimum vent. But, make sure it varies according to outside temperature
• Minimum pipe • Higher base level (remember to reduce it when humidity is good)
• Influences – gradual change over a wide humidity range
• Don’t change it all at once • It probably won’t work
• If it does, you’ll never know what did it
© 2016 FEC Energy
Screens • Humidity control with respect to screens follows the same
principles, whatever the screen type – thermal, blackout, shading.
© 2016 FEC Energy
Does a screen gapped to control humidity still save energy?
0%
5%
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Week No.
%
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kW
h
Weekly saving No screens total kWh Screens total kWh
Started
gapping
YES
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Climate Control Training
21/09/2016
2016 FEC Energy
© 2016 FEC Energy
If we have to gap a screen to control humidity, will it still save energy?
• YES – to a point, if: • The screen is gapped less than 5%
• The vents rarely open
• Generally NOT if: • Screens are constantly gapped more than 5%
• Venting is taking place above them
• In this situation, the screen might as well be opened fully
• Or maybe not?
© 2016 FEC Energy
Gapping – just like minimum vent
• Gap before you vent • To reduce the effect of cold air spilling through the gap
• Maximum screen position <100% • A bit like a fixed minimum vent
• Same limitations – you could have a gap when you don’t really need one
© 2016 FEC Energy
Screen gapping – humidity influence
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Relative humidity %
Gap
siz
e %
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Climate Control Training
21/09/2016
2016 FEC Energy
© 2016 FEC Energy
Humidity gap
• Variable gap – driven by influences
• Start point, first level influence – Humidity
– Maximum 10% gap
– Typically 5% gap, HD range 2.8 – 2.2 g/m3 (85-90% RH)
• Second level influence – Outside temperature
– Smaller gap when it is colder
– Temperature difference >12oC, max 3% gap
– Temperature difference <8oC, max 10% gap
© 2016 FEC Energy
Start End
Maximum screen position 100
RH influence 85 90 -5
Outside temperature 10 5 +3
Wind speed 3 8 +2
ValueRange
Influences on humidity gap • Why was it ‘spot on’ yesterday but not today?
• It’s colder / warmer outside
• It’s windy today
• Depending on the influences available you could end
up with something like this
© 2016 FEC Energy
Screen gapping – the wrong way
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oC
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Pip
e o
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, H
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Greenhouse temperature Greenhouse HD (x10) Pipe temperature Screen position
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Climate Control Training
21/09/2016
2016 FEC Energy
© 2016 FEC Energy
• Screen gapping – the right way
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Greenhouse temperature Greenhouse HD (x10) Pipe temperature Screen position
© 2016 FEC Energy
That’s all for this session
Any more questions at this stage?
