The 70's remain, in the building industry, the low points both in terms of new building and boiler sales.  This led, indirectly, to demands for minimum efficiency levels to be established. From this there developed an efficiency war between European manufacturers which reached its peak in the 80's.

    Unfortunately they were misleading themselves.

In effect, due to improvements in insulation, they were able to reduce boiler losses and therefore paid little attention to optimising the production of domestic hot water.  Yet, at a time when there was a reduction in the requirement for heating, (due to smaller dwellings, improved insulation etc) there was a growing demand in the requirements for domestic hot water.

    Today nobody can afford to make the error  of calculating the heating load and then assuming that this will be sufficient to meet the DHW requirement. Today the heat requirement for domestic hot water often exceeds that for heating. We have already seen that a thin layer of lime on either the cylinder walls or immersion heater can increase energy consumption by 10 to 50%. What point is there in paying the higher price for a condensing boiler, which is 3 to 4% more efficient, when most of our money runs through the tap and down the plughole?

This is why ACV developed the Delta. It is probably the first appliance to put the accent on domestic hot water generation. Its concept is the complete opposite to the traditional system where the cylinder is simply considered to be an accessory of the boiler.  To succeed with this original concept ACV had to be patient and optimistic.

 Who would have been able to forecast at the outset that such an appliance would be as reliable as a traditional boiler when experience had shown that the life expectancy of a direct fired water heater was only 5 or 6 years. In these the layer of lime quickly insulates the combustion chamber from the water which rapidly leads to a reduction in efficiency followed by perforation of the combustion chamber due to overheating. The original idea of introducing a heat exchanger into the domestic hot water to feed central heating circuit was therefore a failure.

    The only solution was to eliminate the wall separating the flue gas passageway from the domestic hot water. The Delta is nothing but a hot water generator which has solved the problems associated with lime deposition by introducing a primary circuit and from this it was only one step to use it as a boiler. 

    To answer the sceptical one can say that the first Deltas are still operating. Moreover the new manufacturing techniques has served to make them more reliable than ever. 

    It is well known that wall hung combination boilers, however sophisticated, can only provide a maximum flow of 9 litres per minute at 45°C, which corresponds to the 16 litres per minute at 30°C (Δt=20°C) listed by manufacturers. If one considers that a standard bath, ready for use, contains  approximately 140 litres then it will take fifteen minutes to fill this. 

    There is therefore, in our opinion, a lack of comfort, some people can live with this, others can't. This is why more and more people are coupling a small storage cylinder to the boiler. Almost all wall hung boiler manufacturers now suggest the use of these additional cylinders to meet the users peak requirements for domestic hot water. ACV, with 30 years specialisation in the preparation of domestic water, decided to commercialise such a tank marketing it as the FastTank. The combination of boiler and tank occupies more space, is more expensive and takes longer to install but at least it provides basically acceptable comfort levels. We remain convinced however that such a makeshift arrangement never comes near to the performance of a Delta. This offers greater comfort (740 litres per hour at 60°С), is easier to install, is easier and cheaper to service, has a higher efficiency and is more aesthetically pleasing. 
    BY COMBINING high combustion efficiency with high appliance efficiency one reduces atmospheric pollution. Acheiving high efficiency means consuming less energy and consuming less energy not only means saving money but also ensuring a better environment for our children to grow up in. 

    We have seen that the Delta is not subject to increasing energy consumption because, like the Tank in Tank there is a little lime build-up.
    In a traditional system the mass of water in the boiler is heated and then flows to the tank along pipes which are as well insulated as practical. A study carried out in a German laboratory has shown that an integrated appliance has an overall efficiency 6% higher than the traditional system. This cannot be ignored and cannot be considered negligible. It should also be remembered that the Delta is fitted with a rigid polyurethane foam insulation whereas nearly all traditional boilers are still insulated with glass wool (clearly a lower performance insulation).