How to benefit from heat load matching in heat networks

Modular boilers with large boiler turndown ratio and wide differential temperatures between the flow and return are rising in popularity.

The challenges of providing heat to a heat network

A commercial heating system is designed to match the peak load to heat a building up to full temperature within a short period of time. This requires a large load from the heat source; the boilers. However most of the time the boilers will be working at much lower loads. So how do you match both demands without oversizing or wasting energy?

The solution for heat networks

A modular boiler system.

But how is this achieved?

Read on to understand how modular boilers offer an affordable, efficient and secure system for heat networks and beyond.

How low can your boiler go?

A boiler installation with a large turndown ratio (ratio minimum to maximum output capacity) meets both peak and low loads with ease without wasting energy. In a typical modular boiler system each module could have a boiler turndown ratio of 5 to 1. So, a vertical stack of 3 modules will have 15 to 1 turndown. This gives you a substantial range of outputs.

For example:

• 1 x 250kW boiler module with 5:1 boiler turndown ratio
• A 3-high boiler stack would be 750kW with a 15:1 boiler turndown ratio.
• This boiler can provide a seamless delivery of energy at any output from 50kW up to 750kW.

This ensures the load is matched to warm the building up. When you’ve got low loads, the modular boilers are not constantly cycling and wasting energy.

Maximum return on investment with minimum return temperatures

This has become increasingly important when designing heat networks where boilers are used with renewables and combined heat and power (CHP).

But why is this?

Heat networks typically have diverse load requirements.  From minimum summer loads when mainly hot water requirements are being met with morning and evening spikes in demand, to winter loads with additional heating needs.

When installing CHP, designers need to look at minimum load very closely as the unit will be running continuously to meet the base load heating requirements.

The boilers will then provide top up to meet peaks in demand at different times. The minimum input from the modular boiler should match the base load covered by CHP. But the boiler also needs to cover the full load to ensure security of supply to buildings in the heat network.

Low loads

During low load conditions it is essential to have sufficient boiler turndown ratio to accurately match the base load without wasteful cycling. But the boilers also need to be running in their most efficient state - at or near their minimum modulation, i.e. part-load. This maintains very high system operating efficiency and the owner of the heat network can produce low cost and low carbon energy.

Increasing heat loads

System dynamics dictate how often boilers actually condense based on return water temperature. Return temperatures will reduce as system loads increase with more energy consumed from the circuit. A modular approach allows the increasing load to be met by more boilers operating at part load conditions. If this coincides with favourable system temperatures, then high part load condensing performance will be achieved from the boiler plant.

As system demands increase, boiler load will increase towards full load capacity. At this point system return temperatures should be low and the boilers will continue to operate in condensing condition delivering an efficient energy supply.

The Movement in Greenwich - Heat network

An efficient match

Modular boilers capable of operating with high differential temperatures can closely match system dynamics throughout the year.

CIBSE Guidance AM12 – Combined Heat and Power for Buildings, makes specific reference to designing district heating schemes or heat networks with a minimum of 30°C differential temperature.

This is to keep flow rates and pipe sizes small, and to maintain a low return temperature, even at low load conditions, for more efficient plant operation.

Larger differential temperatures were originally only possible from high water content boilers. But now modular condensing boilers with low water content, such as our Wessex ModuMax mk3 boiler, operate up to 40 degrees delta T (differential temperature). 

This means you can maximise condensing operation and get further energy and cost savings.

The supporting water pipes and pumps can all be smaller with modular boilers and systems with wider temperature differentials.

Plus, a gas booster is often needed with larger boilers but not with a modular boiler. These boosters can be noisy – something a city centre or residential building is not going to want!

An expandable commercial heating system

Something I see a lot on projects is the phased approach to purchase and installation. In particular when constructing a new residential building or mixed use development supplied by a heat network/energy centre. 

Often only parts of the building are in use when it is first opened until they sell or lease the dwellings, offices or commercial units.

With a modular boiler system, you do not need to purchase and install all equipment straight away, you can add and expand the system as the building fills up. Or you can fit everything at the start but only use the boilers that are needed, switching them on incrementally when more people occupy the building. This helps control costs and energy use.

Our compact modular boilers fit through standard doorways, whereas large output boilers take up more room and must be installed before the building is built around it.

Are you sitting comfortably?

One of the prime goals of a heating system is to provide a comfortable environment for occupants.

Take an office block. The building needs to be warm from the start of the day and then stay warm throughout the day. You don’t want boilers cycling to keep the building warm. With modular boilers they can accurately match the load at different increments/variations.

This creates a more comfortable environment as heating remains constant rather than continuously heating up and cooling down as you would get with a larger single boiler.

A perfect match

To help meet the Government’s energy efficiency targets it’s all about providing the right amount of heat at the right time, with little or no wastage. This means products working in harmony to offer the best solution for each application.

Modular boilers tick all the boxes for heat networks, energy centres as well as basement plant rooms, rooftop plant rooms and city centre developments. This is why I see lots of my projects in central London select modular boiler systems.