Node-HIU Virtual Plantroom
Node-HIU Virtual Plantroom
On the theme of the plantroom, below is a schematic of a heat network taking best advantage of thermal storage and multiple heat sources.
File:multipump.svg.2017_08_31_23_10_53.0.svg
It is an extrapolation of systems we have used for domestic renewable systems, where we may combine low grade heat sources with high grade to drive multiple loads. As a back story, we have some 3000+ custom multifuel renewable thermal storage systems in the field going back a few decades and have got this kind of technology off to a fine art - the Heat Bank (TM) - generally on a domestic level, but occasional forays into commercial, with the largest we have as yet done been Putney Plaza feeding 240 properties using a similar setup (Waste air heat pump, cascade boilers, CHP).
Now we have HIUs capable of delivering a VWART of 16C, we would like to float the following schematic for the groups consideration. It applies to any HIU, not just our own, but is based on HIUs having certain abilities:
1. Tracking primary flow temperatures, which are weather compensated between 50C in Summer and 90C when -15C Winter 8am peak (so not often). The ability to go to 90C on a 1 in 1000 day event overcomes the need to oversize pipework. As the HIU tracks primary temperature it has the capability to drop central heating flow to 35C when needed, or ramp up to 80C - all depending on the network supply temperature. No further weather compensation is required, and radiators/UFH takes full advantage of available temperatures. (limits can be set)
2. Ability to run without keep warm, or a reduced keep warm where longer pipe runs result in excessive DHW delays. Keeping pipe sizing small is again a key to reducing the lengths of pipework kept permanently heated (heat loss).
3. Legionella protection - others may argue but it would be our advice when low temperature keep warm is necessary.
4. Indirect CH connection, or direct connection HIU with mixing feature, to decouple primary and secondary temperatures, to enable distribution supply temperatures higher than the peak radiator/UFH temperature, thereby keeping network pipework to a minimum size.
The goals are to provide a simple, valve free arrangement that can maximise the use of lower grade heat and the COP on heat pumps. i.e. reduce running costs and CO2 significantly.
We also feel the pump-only, header free arrangement, smaller pipework approach reduces capital costs considerably - i.e. it far outweighs the cost of a quality HIU with the necessary functionality.
And there is no single (or even two) component(s) in the plantroom, other than loss of power or a burst, that can compromise functionality.
The higher temperature boiler may typically be a CHP unit.
Solar thermal can additionally be fed into the lower section.
We have taken on board the recent understanding that pumps of a certain category can work against dead heads for considerable time, and be ramped up to 180kPa on signal from remote DP sensors when required. We feel that remaining within this pump group, but using more pumps, adds benefits, including the removal of valves to control network supply temperature.
We would aim for all pipework to be full bore between the plantroom and the HIU, with not a single DRV (regulating valve) on the system - just a thermostatic bypass set to 50C at the top of risers.
The thermal store removed the need for a boiler low loss header, improving return temperature performance.
The baffle plate revered high grade storage - multiple series stores are also an option, and more likely in practice due to height restrictions on stores.
Comments most appreciated from suppliers of heat pumps / boilers and CHP systems.
Note there will be a limit of this system where network pipework can only be varied in temperature (thermally cycled) at a limited rate.
The Point of Variable Temperature Supply
Virtual Plantroom Control
The following is a live virtual plantroom running the appropriate control routines for the system. This is taking live data from HIUs in the real world.
http://heatweb.ddns.net:1881/ui/#/1
Heat Network Calculations for 160 properties
The following calculation estimate how 160 properties can be fed using 54mm main flow pipework, 500kW of heat input, and providing 93% seasonal efficiency.
Network Loads & Diversity
The following graphs shows how DHW load can be spikey, but follows patterns. This is the same HIU overlayed from 20 days data at the 7-8am peak load time. Spikes in demand are met with pump head, medium cycles with supply temperature, and with longer cycles met with use of stored higher grade heat and boiler setpoints.
