Greenhouse sites as heat users

When connecting to a heat network, you should carefully consider the availability of the heat. This will come down to both the energy centre and the other connections on the network – where is the heat coming from and who else is using it?

Heat availability

When connecting to a heat network, you should carefully consider the availability of the heat. This will come down to both the energy centre and the other connections on the network – where is the heat coming from and who else is using it?

Most simply, a heat network consists of a centralised heating asset connected via underground pipework to multiple users. These can vary widely in complexity, size, and heating technology. Although the concept is simple, problems often occur if the system is not both designed and operated correctly. This means proper sizing of the heating assets, pipework, and operating temperatures. This tech update explores some of the aspects that should be considered when aiming to benefit from a heat network, as both a heat user and a heat provider.

Where is the heat coming from?

Heat supplied from a neighbouring industrial site may be limited in the hours that large quantities of heat are available to you, when they are not running and producing process heat, they might not have the capacity to deliver your requirement. Likewise, if you are connecting to a large domestic network, there may be periods in the day when most of the other users are drawing heat, leaving you with a limited capacity. The same can be said for heat networks connecting several similar horticultural sites.

Who else is using it?

It is important to make sure that the peak heat use of the other sites connected to the network do not all line up with your own, or to ensure that the heat generation equipment is large enough so that it is able to cover all peak heat uses at the same time. If you are connecting to an industrial site, you should make sure that either their process heat timing lines up with when you require heat, or that they have backup heating arrangements in place if you need heat out of their working hours.

Temperatures

Available flow and return temperatures are important to know when signing into a heat network agreement, this will vary depending on the heat supplier. Many heat networks try to have a large temperature difference between flow and return temperatures, as this maximises heat delivery and, therefore, efficiency.

It is likely that the available temperatures from your heat network will be predetermined, so you should ensure that your pipes are able to facilitate it before signing up.

Sizing

If you have already built your greenhouse and are looking to join a heat network to replace your current heating equipment, your heat distribution pipework will already be in place. If this is the case, you should be careful to ensure your pump rate allows the amount of heat that you need to dissipate from the pipes, while remaining at the acceptable flow/return temperatures of the network.

Conversely, if you have not yet built your heat distribution network, you can choose a potentially cheaper and more optimised pump rate within your pipes and instead size the pipe diameters to allow you to draw your required heat, while meeting the flow/return temperature allowance.

What happens when things go wrong?

As with all heat delivery systems, a backup option is advisable. This could be in the form of a secondary boiler, installed either at the energy centre side of the network or an isolated system at your end, or a heat storage tank. The latter is the most reliable of those options and an accumulator tank is something that you would likely have to install regardless. If you are able to negotiate a contract with time-variable heat price, you have the additional benefit of being able to charge your accumulator tank during cheaper times.

In the heat network contract, you should check what happens if heat is not delivered when you need it, and whether backup heating equipment is installed.

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