For this case study, we are on a 660 acre farm on the Surrey/Kent borders, comprising a number of industrial units, home and other uses, where once 6000 pigs used to roam.

Garage where local heat plant to be sited

The owners of the farm complex were influential with some of the first biomass developments, and while advising other users over 20 years ago, they fitted a plant in their farm industrial area. Their Farm2000 biomass plant used timber and other waste, and was connected to a large underground steel pipework distribution system. Heat on the lucky units and houses connected to the system was unmetered, and it worked very reliably.

Over twenty years later, the projected lifespan of the system now reached, the owners had a difficult decision to make going forward. The pipework was life expired and the boilers were now corroded. The capital cost to replace the system was high, and it needed constant maintenance due to the wide variety of materials that could be used as fuel. There was also the worry of emissions controls becoming onerous for wood burning plants; something that was ignored until recently in the quest for (so called) renewable energy.

Work starts here

Some importers of biomass equipment, now the renewable gold rush is over, have ceased trading this year or given up selling this type of equipment.

Hot Water & Central Heating Ltd had recently installed an external Navien LPG boiler, and had also in 2020 carried out most of the oil boiler maintenance across the farm. We were asked to design and install a solution to run two houses and a swimming pool, which were part of the old biomass plant consumer base.

Bulk LPG was difficult due to tank clearances, and our customer was familiar with oil fired appliances. The biomass distribution system in this specific area of the site had been backed up by a Worcester 50/70 Kerosene boiler for the last 15 years, so oil was decided as the way to go.

Pipework to other building eg pool and chalet (to be boxed in and insulated)

We recommended Tuffa Bunded steel tanks to our customer, and they commissioned and very competently installed a 3500 litre unit in preparation for the new boiler plant.

The boiler plant was to replace the small backup Worcester Bosch 60Kw unit, sited in a double garage.

Navien LCB700 x 2

We specified two Navien LCB700 28Kw Blue Flame external system boilers, linked to a mixing header. A Tekmar boiler load sharing and sequencing controller was used to cycle the Navien boilers.

The Navien LCB700 28LSX oil boilers are unique in the UK, for a variety of reasons. They are two stage, so will run at 21kw and 28Kw depending on flow and return readings. They run with a blue flame, and give lower NoX readings than any other domestic UK oil boiler. And they are designed around a single stainless steel heat exchanger – there are no mild steel boxes inside this boiler, and no minimum return water temperatures.

The header mixes the flows from the boilers and the various buildings

Made and designed by KD Navien in South Korea, they are market leaders for oil boilers in the US and Russia. In many other markets they run on regular Diesel, as Kerosene is largely unknown for heating abroad.

KD Navien have a huge 4 million a year capacity boiler, water heater and CHP manufacturing plant, probably the largest in the World. They give their LCB700 oil boilers a full 10 year on site UK warranty, without exclusions of any parts, and are based in Guildford, Surrey.

Our customer sensibly chose external grade boilers, even though they were sited internally, to provide minimum standing losses. The external models are extremely well insulated, at only a small price differential from the standard white cased version.

The MikroFill automatic water fill device. The farm pumps water from its own borehole, this comes in at 3.0bar. System pressure is maintained by the Mikrofill at 1.2bar.

We fitted a MikroFill AFD system to keep the water topped up. The Mikrofill AFD makes a regular appearance on our larger installations, because it is the best product in its field.

In the main house we fitted 24 zones of Honeywell Evohome, including the control of a large underfloor installation.

24 controllable heat zones in main house using 2 Honeywell Evohome touchpanels

Other links to the system include a chalet and a swimming pool, all of which can separately enable the boiler plant.

Tekmar boiler cascade management

The two Navien boilers are rotated and managed by the Tekmar sequencer. The second boiler comes in after a 10 minute delay; and only then if the temperature monitoring of the header system shows more horsepower is needed. In this way the system can run at between 21 and 56Kw. At the annual service both boilers will have run for a similar number of hours.

System cleaning with Powerflush and MagnaCleanse

All pipework was in copper, and fully insulated. We managed to get the system into quite a compact format.

Tightly packed boiler system with three separate locations, one of which has 24 zones

The external oil supplies were fed via Tiger Loop units; these pull air out of the oil, act as a buffer reservoir, and also preheat the oil. The Combi Tiger Loop incorporates a visible oil filter and a larger reservoir, all these features are designed to provide a consistent and stable oil feed to the Danfoss oil pumps in the Navien LCB700s, in all weathers.

Tiger Loop oil dearators for each boiler give longer oil pump life, external pipes run to pool boiler room, a duct is to be created later

If you have a requirement for an oil, gas or LPG cascaded boiler system, please get in touch.