Fast and dynamic controls are essential to instantaneous Heat Interface Units (HIUs)!cheetah

Getting the design of district heating and central plant systems right is crucial to achieving low system return temperatures at design conditions. However, as the Heat Network Code of Practice for the UK will emphasise when published later this year, it is important that system return temperatures are kept consistently low also under part load.

 

 

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The central pumps in Heat Networks are constantly ramping up and down to meet the dynamic demands of the network. Typically, the pump pressures spike in the morning and evening, primarily as a result of varying DHW loads.

Even within the individual dwellings the DHW load profile will vary and very rarely reach full load.

closing-time-diagram

silas

Silas Flytkjaer, Product Manager – Danfoss FlatStations

“To generate instantaneous DHW at constant temperatures, under varying tapping conditions – while keeping system return temperatures consistently low – HIUs need fast, self-acting pressure and temperature control valves.”

 

Controlling primary return temperatures from domestic hot water production

Objective: Maximum return temperatures of 25°C from DHW instantaneous heat exchangers. CIBSE AM12:2013, GLA London Heat Network Manual (2014), BRE – A Technical Guide to District Heating (2014) & CIBSE/ADE – Heat Networks Code of Practice for the UK (to be published in 2015)

Challenge: Achieving stable DHW flow temperatures and consistently low primary return temperatures under fast changing dynamic load conditions.

Simultaneous performance graphs for 7 Series DS fully insulated FlatStation

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Danfoss IHPT inside the 7 Series DS FlatStation

The Danfoss IHPT valve is a state-of-the-art self-acting, flow-compensated temperature controller with built-in differential pressure control. It has been developed specifically to control instantaneous DHW. The fast-acting valve not only ensures DHW temperature accuracy during fluctuating pressure, temperature and tapping conditions, but also prevents scaling of the plate heat exchanger by instantly closing the valve controlling the primary supply flow.

circuit-diagram

IHPT – Designed with Self-acting DHW controller to achieve the fastest possible reaction times

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IHPT – Primed 8ºC Temperature Set-back

The Primed Temperature Set-back lowers the temperature at which the plate heat exchanger is kept warm by approx. 8 °C helping to reduce system return temperatures and distribution losses.

Danfoss FlatStations on duty in apartment buildings!

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