In the pipeline

In the pipeline

While major advances have been made in boiler technology  to elicit optimum performance when  burning gas for water heating, installation practices have not always been so quick to evolve. Christian Engelke talks to Installer about the efficiencies and costs savings afforded by installing a four pipe system.

A preference for using an open vent boiler to achieve a pressurised system is a prime example of an ageing installation habit. Installing such units with a standard two pipe system is often seen as the simplest option for replacement fittings – especially considering consumers’ preference for replacing like with like. However, while this may be the most obvious choice initially, it is not necessarily the cheapest or most efficient option in the long term.
Viessmann’s four pipe system – available across its Vitodens range (available in 19 kW, 26 kW, 30 kW and 35 kW outputs) – is an innovative alternative. The system allows the boiler to discriminate between the hot water (DHW) and heating circuits, serving each circuit with separate flow and return pipes. This means energy cut-off valves are no longer required.
In addition, cylinder overheat thermostats are not required in Viessmann’s four pipe system as a DHW sensor fitted to the cylinder controls temperature and satisfies the necessary G3 building regulations.
Alan Betts of Alexandra Heating Services Ltd, a Viessmann installation partner, believes that the four pipe system is the perfect combination to meet G3 Building Regulations.
“Installers and customer benefit from Viessmann’s solutions to delivering outstanding performance from a four pipe system boiler operating with a hot water cylinder. With environmental issues uppermost on the agenda, high efficiency condensing boilers running at lower flow and return temperatures are not best suited to Y or S plan two pipe systems.
“As installers of Viessmann’s portfolio of products, we opt for the highly efficient four pipe Vitodens
100  and  200  range  of  boilers  in  conjunction  with  the  Vitocell  range  of  domestic  hot  water
cylinders.
“When fitted this allows for higher flow and return temperatures to cylinders for quick recovery time and lower flow and return temperatures for heating, ideal when also using the Viessmann weather compensating control for additional savings in running costs. By installing a Viessmann four pipe boiler and unvented cylinder, the G3 Regulations are met, which saves time and installation costs. This system is ideal for new build and the replacement markets alike.”
Aside from the cost savings, the additional benefit of installing a four pipe system is being able to specify a lower output, more affordable boiler. In a normal S or Y plan system the boiler is typically oversized by 10 – 30% (or 6-10 kW) in order to cater for the hot water demand.

Both the S and Y plan system run on two pipes, meaning the boiler is providing both hot water and heating at the same time. This creates a need for a greater output than each individual circuit would require  and  a  higher  temperature  than  may  be  required  for  heating.
One of the big disadvantages is that this type of system does nothing to improve overall system efficiency. With the Viessmann four pipe system, the boiler satisfies either the heating or the hot water. When both are required, the boiler prioritises hot water to ensure its immediate availability and continues to re- heat the cylinder as it is being used.
The principal advantage of the Viessmann four pipe system when it comes to the heating circuit is that it allows weather-compensated controls to be fitted. A weather control monitors the outside temperature and adjusts the flow temperature for the separate heating circuit. This balances the heating requirement to the anticipated heat loss to maintain the desired room temperature.
Weather compensation the efficiency of the boiler can be improved by up to 15% as the boiler will condense when possible. The dew point for the flue gases is between 55-57 ⁰C, therefore a flow temperature below 57 ⁰C means the water vapour in the flue gases will start to condense and deliver the additional efficiency gains that a condensing boiler is designed to.
Operating at a reduced flow temperature also means that longer firing periods are possible and cycling is reduced – both of which are instrumental in optimising efficiency.
With a four pipe system, an existing 26 kW output boiler can be reduced to a 19 kW boiler. This will deliver not only a cost saving to the home owner, but also – when installed with weather compensation – improved levels of comfort in the home. For the homeowner, the savings more than offset the extra cost of converting a standard two pipe system to a new four pipe system.
In a competitive market, it is understandable why some installers may be nervous about proposing product and system innovations to their customers. However, as the four pipe system demonstrates, the end result is often considerably more favourable.
In a similar way, the change from open vent to combi boilers delivered energy efficiency gains by heating DHW on demand rather than producing hot water at the same time as the central heating and storing it in an old and inefficient copper cylinder.
Furthermore, innovations such as weather compensation controls adding real value to the customer, and offering these technologies is a key differentiator for installers from their competitors.
Viessmann  believes  recognition  of  the  four  pipe  system  in  the  Building  Regulations  is  a  huge opportunity  for  the  UK,  ensuring  that  homeowners  would  receive  the  best  solution  for  saving running costs and delivering long-term energy efficiency.