Hot Water Heating Systems
The optimum heating system for larger or muti-zoned greenhouses is a Hot Water Heating System and is typically used on glasshouses requiring more than 8kw of heat. It utilises medium weight finned galvanised steel pipes, a well developed control system, providing accurate temperature settings, even heat distribution and reliable components. All this together with a quality boiler ensures, this the best way to heat your glasshouse. Our heating engineer is experienced in designing a system that will suit a customers individual requirements. Contact us with details of your glasshouse, so we can calculate the heat load requirements and provide a quote.
Harrier GD Hot water Systems:
- Are suitable for glasshouses 30m2 and above, multi zoned greenhouses or where high temperatures are required.
- Are the best system when high temperatures are required or when the outside temperature is very cold.
- Are designed specifically for your particular glasshouse. Take time to consider what you want to grow: ‘What temperature do we need?’
- Use galvanised steel pipes which have been selected for their strength, longevity and heat output.
- Have pipes typically mounted around the edge of the glasshouse where the cooling takes place or within ducts positioned in front of soil planting beds.
- Use accurate air temperature sensors for precise control, and which is beneficial for fuel economy.
- Are made up of several key quality components: Heating Pipes, Mixing Groups, Controllers, Aspirated Sensors & a Heat Supply
Steel Finned Heating Pipes
In a greenhouse, the system needs to last in a hot, humid and aggressive environment, so we use high quality galvanised steel pipes, which are ideally suited for this. They are heavy duty, can be stood on covered in mud and water, and carry a 10 year guarantee. The pipes are located, to distribute the heat efficiently and evenly and are finned to give the high outputs required.
Pipes are installed around the perimeter of the glasshouse which is where heat is lost, and/or in heating ducts in the floor covered by cast iron grates. (More information on grates can be found in ‘Greenhouse Fittings’.) They are attached to the wall on galvanised steel arms to give a secure fixing.
The heating pipes typically run at a temperature of 82 Deg C giving a high heat output, but is variable unlike electric heating. However, they can run on lower temperatures, if a heat pump is being used. Other benefits are this method of heating does not spread bacteria like forced air, and its quieter to run.
The length and number of pipes required will be calculated by our heating engineer for each individual project.
Heating power needs to be supplied to the pipes, and can be provided by any source that gives a flow and return of hot water. Traditionally the water has been heated by high performance boilers, oil or gas fired, to suit customers requirements and preferences. They are reliable, well made and normally positioned in an adjacent potting shed or boiler house.
They operate at 82 Deg C. This temperature works well in heating the air around the pipes. Once the section of the greenhouse has reached its target temperature, the boiler will shut down, thereby saving fuel.
Occasionally an electric boiler is selected by a customer. They are small and have no exhaust/flue requirements, and are quiet to run. However, they do have high running costs.
More recently, customers have requested a greener solution. We have installed Ground Source Heating, Biomass Boilers and utilised electrical power from hydroelectric turbines. These are more fully explained in our ‘Sustainable Heating’ section.
Control Pipework – The Mixing Group
The heating for a glasshouse needs to be designed well to avoid huge swings of temperature, which would not be good for the plants or fuel economy. In a typical domestic house heat is turned on and off as required, and no modulation is required as the power requirement is relatively low, and the thermal heat capacity is high. Unfortunately, this is not the case in a glasshouse, so to achieve the heating demands, we modulate or change the temperature of the heating water in the finned pipes.
This is achieved using a giant shower valve, so the temperature of the pipes changes depending on the heat load, giving good heat distribution. The system keeps circulating when no heat is required; this gives even cooling in the glasshouse. Another problem with a glasshouse is that heat demand can go from full power to off very quickly, for instance when the sun comes on a glasshouse on a cold winter’s day. For this reason we have a quick response valve and settings are tailored to each glasshouse.
The control pipework is modulated from a Harrier Heating Controller and an Aspirated Screen. The Mixing Group also includes temperature gauges, to monitor pipe temperature, isolation valves and unions to aid maintenance, and a by pass depending on the application.
Harrier Heating Controllers
Harrier has developed two high quality controllers designed and manufactured for their greenhouse heating systems – the HH2 and the HH3
The HH2 controller has been designed & developed specifically by Harrier to accurately control the climate within a glasshouse. Being the market leader in this field, gave us the insight into exactly what was needed!
- The HH2 will control both Ventilation AND Heating within the glasshouse.
- It is made to an IP65 standard (water & dust proof) so the units will last for many years in the harsh and humid environment of a glasshouse.
- The unit has been designed to be intuitive and easy to operate
- Different temperatures can be set between day and night – many plants thrive if the temperature is lower at night, and this saves fuel.
- It has a digital readout to assess the current temperature and easily change it if required.
- It has manual overrides which offers a handy way to temporarily open the vents or turn up the heating.
- The operational parameters of the ventilation and heating are set when commissioning the greenhouse to give the best response from both the heating and the ventilation, whilst using the minimum fuel required.
In order to maintain accurate temperates within a structure the controller needs accurate temperature readings from within the glasshouse, and this is the function of the Aspirated Screen.
- The Aspirated Screen contains a temperature sensor mounted in a box with a circulating fan. The fan draws air across the sensor giving an average air temperature, and avoids inaccuracies, for example if the sun shone directly onto the sensor.
- It is typically hung from a chain where the plants are (either above a bench or in planters) because this is where you want the temperature to be maintained.
- Aspirated Screens are also rated IP65 and are supplied as standard with a controller.
It has been developed more recently because we found the functionality of the HH2 Controller was not needed in all cases. A smaller greenhouse may have heating with manual vents, or no heating at all but with electric ventilation. In these cases the HH2 is not necessary, and the HH3 would be better suited.
- Automatic or Manual settings are available.
- The HH3 is IP65 rated to withstand the harsh and humid environment within a greenhouse.
- It has an easy to understand digital readout showing set or current temperatures.
- A remote temperature sensor is supplied as standard with these units, giving accurate feedback to the controller which is required to maintain set temperatures. The sensor, being remote can be hung from the roof near the plants.
Servicing & Maintenance
It is advisable that all Hot Water Systems should have an annual Mechanical & Electrical Service to ensure they run efficiently. Please contact Harrier GD to organise an Annual Service Contract.