- Energy Saving
What is your minimum pipe temperature setting?
Reducing minimum pipe temperature settings is a good way to save energy. However, this must be done alongside well considered ventilation settings to ensure that heating requirements are minimised.
The example below shows what happened at one of our Focus Nurseries where humidity influences and minimum ventilation settings were reducing the effect of a good minimum pipe temperature strategy.
Minimum pipe settings
In an attempt to save energy, Red Roofs Nursery has been using a minimum pipe temperature setting of 35 degrees C, which reduces when solar radiation increases. This setting remains unaffected by relative humidity changes.
At first glance, this looks like a good energy saving strategy; however a closer examination of the climate graphs shows that things might not be quite as good as we think.
(Click on graph to see a larger version)
This graph shows that between midnight and 7am the pipe temperature averaged 60 degrees C, and the vents were also open for a significant proportion of the same period.
Why did this happen?
Humidity influences were being used which caused the heating and ventilation operational temperatures to converge when the relative humidity was increased.
As such, the minimum pipe temperature setting was effectively overridden and had no bearing on the heating inputs or ventilator positions.
As a consequence, heating was being applied at the same time as the vents were open.
And what did it cost?
Running an extra 25 degrees C of pipe temperature for 7 hours in a 1 Ha greenhouse led to the extra consumption of 7,650 kWh of gas. Even with gas prices at around 1p/kWh (assuming day-ahead buying), this still represents £76.50/Ha/night!
Solving the problem!
- Ventilation temperature setting – make sure that the ventilation temperature is always at least 0.2 degrees C above the heating temperature. This setting should be maintained all the time, even if the relative humidity is high.
- Minimum ventilation settings – use these sparingly and reduce the amount of ventilation when it is cold outside.
- Relative Humdity = 85% Minimum Vent = 0%
- Relative Humidity = 90% Minimum Vent = 2%
Or, if you are controlling humidity based on humidity deficit (HD):
- Humidity Deficit = 2.7 g/m3 Minimum Vent = 0%
- Humidity Deficit = 2.3 g/m3 Minimum Vent = 2%
Also, use outside temperature influence on the minimum ventilation so that the opening reduces by half (i.e. a maximum opening of 1%), as the outside temperature falls from 12 degrees C to 8 degrees C.