Tag Archives: control

Measuring CO2 in a Greenhouse

CO2 in Greenhouses in General

CO2 is one of the key ingredients of photosynthesis, meaning it is essential for plants to grow. Monitoring CO2 in a greenhouse allows optimisation of plant growth conditions, resulting in more efficient plant growth and higher crop yield. Different plants need different levels of CO2 in the air to maximise development.

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Facts & Figures

One of the largest greenhouses in the world is in Almeria, Spain where greenhouses cover almost 50000 acres (200km2)

In the Netherlands, greenhouses occupy 0.25% of the total land area.

The Netherlands has around 9000 greenhouse enterprises that operate over 10000 hectares of greenhouses and employ some 150000 workers: 80% of the manufactured produce is exported.

Why The Need to Measure CO2

It is essential to monitor CO2 levels at all times because different plants have different needs regarding CO2. Before photosynthesis, CO2 is collected by the enzyme RuBisCO. However, RuBisCO is just as happy to collect O2 as it is CO2. In C3 plants, RuBisCO collects CO2 from the air as soon as it comes through the stomata on the leaf. This means that if levels of CO2 in the air are low compared to levels of O2, the RuBisCO will just collect more O2 and the plant growth will be less efficient. In a C4 plant, there is an extra step during which CO2 is ‘filtered’ from the air and passed on to the RuBisCO. During this extra step, CO2 can be stored, meaning the stomata do not need to be open all of the time, helping to prevent water loss. In the C3 plant, the stomata need to be open more as there is not such storage of CO2. A third kind of plant, a CAM plant, can only collect CO2 at night, as its stomata are closed during the day.

Tomato_leaf_stomate_1-colorStomata on a tomato leaf

It is important to have close control of the ventilation of a greenhouse to utilise CO2 to maximum effect without risk
of damaging plants. Generally, the best practice is to provide increased CO2 to young plants and parent plants regularly, and to all other plants for a short period during spring. If the plant is sensitive it is extremely important to have pure CO2, to prevent damage. Up to 1 000 ppm CO2 is estimated as a good level.

If the levels of CO2 are too high in the greenhouse, plants can be damaged. If CO2 levels rise too high, plants will close their stomata to protect themselves, resulting in less transpiration, and therefore less nutrition is drawn through the plant, slowing down growth. CO2 levels vary considerably over a 24 hour period. This is because during the night, plants can stop photosynthesis (in the absence of light) and begin respiring. this means plants will switch from using CO2 to producing CO2.

plantsWhen there is plenty of light, a plant will photosynthesize, but when light levels are too low plants will begin to respire instead

What is the Result?

If all plants of a crop are grown in the same conditions (including CO2 levels), the chance that all plants will be ready for harvest at the same time is increased. The annual consumption of CO2 in a greenhouse is generally about 5-10 kg/m2, only in exceptional cases does would it be higher. The effect, of using CO2, on profit varies considderably. For example, tomatoes and cucumbers can give 8-10% higher return when growin in optimal CO2 levels. Plants grown in a CO2 enriched environment generally produce greater biomass than other plants, particularly in the roots, allowing faster growth and resulting in stronger plants with an increased reproductive rate.

Philip Robinson                                                                                                       Rotronic UK

CO2 and Indoor Air Quality (IAQ)

Indoor Air Quality in General

The quality of the air in a room can greatly affect the health, productivity, and well being of any occupants. Previously the temperature and humidity of indoor air were considered as the most important parameters contributing to air quality, but there are several other factors which must be taken into account.

Indoor Air Quality (IAQ) problems are very often caused by gases or particles released into the air by pollution sources. This can be avoided by carefully selecting the materials which are to be used inside dwellings, offices, classrooms, gymnasiums, hotels, shopping malls, hospitals and in all en-closed spaces which are inhabited. But there is another source of air pollution, which cannot be avoided. this other source is people themselves. Every time a person exhales, CO2 is released. Inadequate ventilation may increase CO2 concentration to an unhealthy or even life-threatening level.

carbon_dioxide_3d_ball

CO2: made up of 2 oxygen atoms, double bonded to a single carbon atom.

The most important control parameters for a good Indoor Air Quality are temperature, relative humidity and CO2 concentration. If these values are used with an intelligent air conditioning system, an energy efficient air supply can be used to produce a high quality atmosphere.

Facts & figures:

CO2 is a naturally occurring molecule consisting of two oxygen atoms and a single carbon atom.

At standard temperature and pressure CO2 is a gas, invisible and without any smell or taste.

CO2 is 50% heavier than air and has no liquid state under atmospheric pressure.

In the earth’s atmosphere CO2 has a concentration of 390 ppm by volume.

The worldwide industry produces approximately 36 billion tons of CO2 per year.

Industrial activities are responsible for an increase of atmospheric CO2 concentration and thus for an increase of global warming (greenhouse effect).

Influence of CO2 on Humans

Only a small amount of the atmosphere is made up of CO2, the prevailing components are nitrogen and oxygen. The natural outdoor atmosphere CO2 level is approx. 390 ppm. Increasing this concentration causes several symptoms of poisoning, ranging from drowsiness at around 1´000ppm to unconsciousness and even death at above 10´000 ppm. Even if a  rise in CO2 concentration has not yet severely influenced the health of people, it may reduce their productivity, efficiency and well-being.

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Some of the possible health effects

How to Measure CO2

The most common measuring method for CO2 concentration nowadays is based on a spectroscopic principle. Sending infrared light (IR) with a wave length of 4.23 μm through a gas sample. CO2 molecules in the sample absorb the light at this wavelength. an IR sensor is then used to detect any changes in the energy levels of the light after passing through the sample. The more C)2 in the sample, the more of the light that will be absorbed, and the weaker the IR signal will be when it reaches the sensor.

ndir-sensor_1

Example of an IR CO2 sensor

The sensitivity of a CO2 sensor increases with the length of the light path through the sample gas. Thus the sensor used in Rotronic CO2 measuring devices makes use of multiple reflections of the IR beam on the walls of the probe chamber. this means the small CO2 sensor (2.5 cm x 5 cm) has a measuring path length of 12.5 cm and is accordingly sensitive. This type of sensor is called a NDIR (Non Dispersive Infra Red) sensor. This means that a broadband IR light source is used and the measured wavelength is filtered out at the end of the beam in front of the IR detector.

Why the Need to Measure CO2

New energy efficient demands lead to more airtight buildings and ventilation being completely turned off at night. Intelligent HVAC systems must be able to adapt themselves to situations with changing occupants of rooms. One answer is Demand Controlled Ventilation (DCV) with built-in CO2 sensors. By using DCV, huge amounts of energy can be saved without any drawback for the occupants. According to a study of the UN Climate Panel 40-50% of world energy is used in buildings. Only the adoption of the EU Directive on Energy Efficient Buildings would result in saving 30-45 MT of CO2/year. As HVAC (Heating, Ventilation and Air Conditioning) is responsible 40-65% of energy usage in commercial and public buildings, a balance between comfort and energy saving must be found.

HVAC

A large HVAC system

One example demonstrates the evidence of CO2 controlled room ventilation. The exhaled air of a human contains up to 40´000 ppm CO2. In one hour a person breathes out 15 litres of CO2. Thus in a classroom with a volume of 200 m³ occupied by 25 pupils the CO2 concentration increases in one hour by 1´875 ppm!

Especially in wine cellars, breweries, the beverage industry and other industries in which CO2 may be produced or processed the constant measuring of CO2 concentration is absolutely vital to prevent a deadly threat to the employees. This is not only a rational procedure but is also enforced by official regulations in nearly every developed country.

Philip Robinson                                                                                                       Rotronic UK

Chicken Hatcheries.

As it is nearly Easter, I thought it would be a good idea post something related to eggs, unfortunately not the chocolate kind…

Chicken hatcheries in general

It takes about 21 days to hatch a chicken and during that time, it is crucial that the surroundings are controlled for it to be successful. Egg hatching farms transform the chickens into “broilers” or egg laying hens. Meat from egg hatching farms is the most consumed worldwide.

Facts & figures:

Approximately 49 billion chickens are consumed worldwide every year. That is 134 million every day.

Chicken is the most common type of poultry in the world.

100g of baked chicken breast contains 4 grams of fat and 31 grams of protein.

Sustainability of chicken meat increases by 20%, when using CO2 for modified atmosphere processing.

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Why the need to measure CO2?

Less staff required to run the breeding stations thanks to all hatching happening at around the same time. This means it is easier to plan shipments and know how many birds can be transported at a time. This results in less capital and reduced transport costs.

A smaller number of birds die during transportation, which results in more profit per shipment and less feed losses.

More efficient and cheaper feeding options, both through feed reduction and reduction in time.

Chickens_eating

Faster and easier to slaughter the animals using CO2, and there is no unnecessary suffering to the birds.

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Packing using CO2, means food will last longer in supermarkets and for customers once purchased. This means a reduction in food waste from expired food.

How does it work?

The fertilized eggs are placed in a chamber, in which CO2 levels are controlled, depending on what stage of development the eggs are in. Living eggs contribute to the levels of CO2 (not 100% of all eggs are alive), which means that you have to monitor the CO2 continuously.

It has been shown that during embryonic development, the supply of CO2 has positive effects on the health of the organism after birth. Control of CO2 in chickens in development has also led to a more controlled hatching time.

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Once CO2 levels insid an egg reach a certain level, the fully developed chickens start to hatch. When the chick has hatched, oxygen will be supplied. Once the eggs are hatched, they are sent off in trucks where the birds continue to develop during the transportation. To ensure the good health of the chicks during their transportation, the CO2 levels in the truck are controlled for the whole journey.

It has been found that a bird’s metabolism works slower at high concentrations of CO2. Controlling CO2 levels therefore means it can take less time and less food to raise broilers or egg laying hens. This means production will be cheaper for the companies, it´s also more sustainable to use less feed per pound of chicken.

The chickens are slaughtered after being knocked out with high levels of CO2, which only take a few seconds. This method is more humane than killing by electrical stunning.

Philip Robinson                                                                                                       Rotronic UK

Energy Efficiency and Reliability in Modern Data Centres

Introduction

Data centres are rapidly becoming the power houses of the modern world. Combined with the rise of digital industries, virtually all business operations now rely in some way on the transfer of data. As data transfer rates increase in tandem with an explosion in mobile communication the demands on data centre infra-structure are ever increasing.

It is estimated that by 2018 global data traffic will exceed 8500 exabytes (32% compound annual growth rate).

Data centres provide the infra-structure to support the transfer and hosting of data. They are often classified into 4 tiers. Tier 4 provides highest levels of redundancy, security and efficiency. For example, a Tier 4 data centre is required to have an uptime of 99.995% equivalent to less than 27 minutes downtime per year! Tier 4 sites have fully redundant systems, power supplies and biometric security. Zero downtime is the ideal as the costs incurred via end user penalties can be huge.

data centre tiers

Why the need to measure temperature, humidity and differential pressure?

Data centres must be maintained to specific environmental conditions to ensure the performance and longevity of the hardware installed. As standard, temperature must be 18-27 °C, dew point 5-15 °C dp and humidity no higher than 60 %rh. This ensures the hardware is at a suitable temperature, condensation is avoided and the chance of static build up is reduced (caused by low humidity).

A control range of ±9 °C may seem relatively broad, however 100% of the energy supplied to server hardware is converted to heat. In most data centres if the cooling system fails and servers are not shut down, heat levels will rise above a critical 35 °C within minutes or even seconds. If unchecked, temperature levels will rise causing hardware damage and can result in electrical fires.

Achieving the specified control range requires precision sensors and advanced control systems. Typically modern data centres are designed using computational fluid dynamics to ensure the very highest efficiency. Despite this it is estimated around 5% of US electrical energy used is for data centre cooling.

pue power usage effectiveness

Since 100% of electricity utilised by servers is converted to heat, theoretically a 100% efficient cooling system would require an equal amount of energy. Efficiency is measured by comparing total facility energy use, with IT equipment energy use. This is called Power Usage Effectiveness (PUE). Theoretically PUE can be 1 but typically reported values are above 2. By utilising precision measurements and design, modern data centres achieve PUEs of ~1.1!

An improvement of 0.5 in a data centre’s PUE  equates to a energy saving of ~£2.2 M & ~12,000 tonnes CO2 over 5 years (for a site with 1 MW load).

 

What solutions can Rotronic offer?

Rotronic provides a range of instruments for environmental monitoring and control. Reliable and precise outside air sensors and weather shields enable natural cooling to be utilised where possible.

Inside the data centres, Rotronic interchangeable HC2-S probes can provide a combination of precise, fast response temperature and humidity measurements with ease of calibration. Our latest PF4 differential pressure transmitters provide precision low drift measurements.

With both digital and a range of analogue outputs available as well as several probe mounting options, products can be selected for all applications.

Importantly though we aim to understand your needs and build a relationship with the goal of providing an appropriate solution, combining instruments, training, calibration and ongoing support.

Dr Jeremy WIngate
Rotronic UK

 

Timber Drying

We recently visited a company which is involved in the drying of wood, and learned a bit about wood drying. This company had bought a temperature and humidity logger for monitoring their drying environment.

Timber Drying in General

Wood is probably one of the oldest building materials on the planet. But before wood can be used as a construction material, whether it for structural support in a building or to manufacture furniture, it has to undergo treatment to gain the required properties defined by the application in which the wood is used. The first and most important treatment is the drying process.

MINOLTA DIGITAL CAMERAA timber frame for a barn.

The fastest and most effective way to drying timber is in a Kiln. Kiln drying is done in a closed chamber in which air temperature, relative humidity and airflow can be controlled to dry timber to a specified moisture content. The temperature for the drying is usually between 40-90°C depending on type, size and the intended use of the timber. There are many different types of kilns such as vacuum systems, traditional heat and vent type kilns and radio frequency dryers. The cost of installing and maintaining a kiln may often be prohibitive unless a large amount of timber can be processed. However, if the value of specific species is high enough, it becomes more feasible to kiln dry green timber.

Drying_process2Wood in a drying kiln.

Some other drying options timber include: Solar drying where the green timber gets put into a glass house. This option is more often used for drying small amounts of timber. For bigger amounts the Air drying option tends to be used more often. Both drying options are only controllable to a very limited extend since they strongly depend on weather conditions.

Facts & figures:

One cubic metre of freshly felled oak contains approximately 540 litres of water.

Examples for air drying times:

Softwoods: 25mm thick Scots pine that is stacked in April can reach 20 % moisture content by July to August if the summer months are warm and dry.

Hardwoods: 25mm thick English oak if piled in early autumn can reach 20 % moisture content in about 10 months.

A 75mm thick log of wood can even take 3 years to reach equilibrium moisture content.

Why the need to measure humidity?

Controlling humidity during the timber drying process is essential for many factors. An incorrect level of % Equilibrium Relative humidity (ERH) in wood can have the following effects on product and process:

OLYMPUS DIGITAL CAMERAWhen damp, wood is easily damaged.

Dimensional changes

A controlled drying process prevents the timber from unacceptable shrinkage after the installation. But since wood is a natural hygroscopic product it will always change its size to a minor extend.

Strength

Drying the timber below a water contents of 25 % to 30 % will maximise the mechanical strength. dry wood is nearly twice as strong and twice as stiff as green wood.

stess_moisture_plotAs moisture content of wood decreases, the strength increases.

Decay

After drying, timber maintaining less than 20 % moisture content is unlikely to be attacked by wood decaying fungus.

Preservation

To increase the effectiveness of preservative treatments. Many preservatives should only be applied when the humidity of the timber has been reduced.

Corrosion

Drying timber prevents the corrosion of metal fixings such as  nails and screws.

rusty-fixingsWhen wood is wet, it may corrode metal fittings.

Weight

Dry wood is much lighter in weight than wet wood. For many species, dry wood is nearly half the weight of wet wood.

Philip Robinson                                                                                                           Rotronic Uk

Humidity and Seed Storage

I recently visited a facility where they were doing a lot of research into plant biology. As such, it was important for them to have their seeds stored at exactly the correct temperature and humidity to prevent germination or degradation of the seeds.

Seed storage in general

Around 10000 years ago when the first human beings stopped hunting and gathering wild plants, and started to cultivate on farms, preserving and storing seeds became important.

There are various reasons to store seeds, for example, simply preserving grain for consumption later in the year or for sowing during the following season. A little more complex is the collection and preservation of seeds for a longer period of time. This may be done to protect species from extinction or to ensure genetic variety for future generations. Long term storage is also necessary as a back up in case of catastrophic events, such as natural disasters, and disease outbreaks. This type of long term storage is usually done in well protected storage building called seed banks.

Seed-Diversity-in-the-Mil-007A range of seeds in storage

Inside each seed is a living plant embryo which, even in a state of dormancy, breathes through the exchange of gases across its membrane, and is constantly undergoing metabolic processes, also known as aging. The natural lifespan of a seed is influenced by several factors including: permeability of the seed coat, dormancy, and seed physiology. But one of the most important factors is the external environment the seed is exposed to. Temperature and humidity play a key role in the storage capabilities of seeds.

Facts & figures:

The oldest seed that has grown into a viable plant was a Judean date palm seed about 2,000 years old.

The Millennium Seed Bank Project in the UK is the biggest seed bank in the world. Currently they store 31880 species and 1`907`136`030 seeds.

China, with 197 million metric tons, is the world`s biggest producer of rice.

 

Why the need to measure humidity?

Controlling the environment in seed storage is essential for maintaining the germination capacity of seeds, or simply the quality of the seed as a food.

iregi_siteSunflower seeds

In General

Every 1% decrease in the moister content will double the storage life. The same applies for every 5°C decrease of the storage temperature.

A rule of thumb: the sum of the temperature in degrees F and the % relative humidity should be less then 100 for good seed storage conditions.

Storage conditions

Proper storage conditions maintain relative humidity levels
between 20% and 40%, giving corresponding seed moisture contents between 5% – 8%, depending on the type of seed. This range is safe for most seeds. When seed moisture content drops too low (<5%), storage life and seed vigor may decline. When seed moisture content goes above 8%, aging or seed deterioration can increase. Deterioration effects the integrity of the cell membrane, along with several biochemical processes, which overall results in loss of vigor and viability. Seed moisture contents above 12% will promote growth of fungi and insects. Most seeds cannot germinate until seed moisture contents go above 25%.

seedgrowthA newly germinated seed

Seed preparation for long term storage (Seed bank)

To prepare for long term storage, seeds are first put in to a drying room where temperature and humidity is carefully kept at 15°C and 15% relative humidity. Under these conditions the seeds gradually dry out. They are then cleaned, counted and put into airtight containers, before being placed in a seed bank at -20°C. The seeds are then tested for viability on a regular basis.

Philip Robinson                                                                                                                        Rotronic UK