View Full Version : bivalent systems

15-03-2012, 05:18 PM
Hi guys,

what is you're experience whit bivalent systems, for example the combination; gas-heating/heat pump or oil-heating/heat pump and so on.

how do you combine them? in calculations i mean. is it 30% / 70% and most work is for the HP or the other way around?

don't here much about the absorption heat pumps here, are they so perfect?:cool:

love to here from you all,


16-03-2012, 09:36 PM
They work well on air to water systems where the oil/gas only kicks in when the outside temp drops below zero. They don't make any sense where they work in tandem on rads etc as the oil/gas ends up running constantly and the heatpump almost never.

cool runings
18-03-2012, 11:19 AM
The heat pump should be sized accordingly and the back up heating is
only called on if the ambient temperature drops to a point where it
can't cope unaided.

There are many ways of controling this but the true bivalient system brings
in the alternate heat source as the heatpump gets less effiecient and they run
in parrallel (together) until the ambient drops to a point that the heat pump
is inafectual.

All the best



18-03-2012, 11:35 AM
Nearly all the HPs in the USA are dual source, especially the American made ones (not so much the Mitsis) and they have preset change over temps, typically from 0C to -5C depending on where you are in the country. There is no rule for the changeover temp but because they almost always heat through their ducted system, homeowners don't want the cooler air blowing. The only way to really fix it easily is to shut it off and turn on the gas.

Glad i follow the European way heating water:D

30-03-2012, 12:35 PM
Absorption system gets a 'COP' of nearly 0.7

16-04-2012, 08:11 AM
I built my own system using a decomissioned Mitsubish unit and 100L water tank as a buffer. The idea was to pre-heat the water before it went to the boiler (oil) and then onwards through conventional (aluminium) radiators.

It worked fantastically well over the winter. I reduced my oil consumption by nearly 90%. The boiler was only used for about 6 weeks. It's not a fully automated system (maybe I'll do that sometime) but my experience of combining the two heat sources has, from my point of view, proved that it can work extremely well.