Johnson & Starley Aquair Heat Interface + Combi boiler - replacement for current Warm Air system

FreeBear

boulderman said: Gas Safe Register visited and said no to heat pumps as literature cannot state they save money as they do not.

Gas engineers have a vested interest in installing gas powered heating systems. Likewise, a heat pump specialist will also be biased towards their preferred product portfolio. That leaves us, the end user, having to pick through the "facts" ourselves and coming to an informed decision.

Looking at the performance of some of the heat pumps over at https://heatpumpmonitor.org/ quite a few of the systems are on par with gas boilers.

edwardrw

We have an Aquair unit with a Valiant boiler. The installer set it up to run at 60degrees and it spins up from 45 degrees. The boiler will go up to 80 but it isn't neccessary for our, 4bed, house which is fairly well insulated, with a B- EPC certificate. The previous owners added an extension with no wall insulation. 
We are on Octopuss' Gas tariff and their app shows us using 5.6 kW per hour at 60 degrees and it will go onto 80degrees. It goes up to 80, with this setup, only when any hot water/shower is needed.
The downside is that it shuts off when it reaches the set temperature and then loses that warm feeling, before cycling on again.

A heat pump appears to modulate the temperarure rather than turn off, which, hopefully, make it consistently warm. A 23c and less will activate the Aquair cooling effect in summer. The Daikin Altherma medium temperature monobloc meets the criterea . With a water temperature up to 60˚C (down to -7˚C ambient temperature)
There are probably more, but we have just started looking.

FreeBear

edwardrw said:

We have an Aquair unit with a Valiant boiler. The installer set it up to run at 60degrees and it spins up from 45 degrees. The boiler will go up to 80 but it isn't neccessary for our, 4bed, house which is fairly well insulated, with a B- EPC certificate. The previous owners added an extension with no wall insulation. 
We are on Octopuss' Gas tariff and their app shows us using 5.6 kW per hour at 60 degrees and it will go onto 80degrees. It goes up to 80, with this setup, only when any hot water/shower is needed.
The downside is that it shuts off when it reaches the set temperature and then loses that warm feeling, before cycling on again.

The following will depend on the model and age of your boiler - Newer boilers with the Vaillant eBus can reduce the flow temperature approaches the thermostat set point. If set up correctly, the boiler should modulate its output down to a minimum and reduce the short cycling. But minimum output will depend on the specific model you have. You also need a smart(er) thermostat that can talk to the boiler rather than basic (and crude) on/off control.

I have a Viessmann combi that, depending on difference between set point and room temperature, runs at between 40°C and 60°C. Power output varies between 8-9kW at start up, dropping down to 4-5kW as the house heats up.

That said, if you are logging 5.6kWh of gas usage, you're probably generating 5kWh of heat, so probably already running close to minimum boiler output. Pretty good for a 4 bed house.

One side effect of running at a low flow temperature is that it reduces corrosion and the build up of scale - Both will contribute to long term reliability. And quite frankly, you don't want to be running as high as 80°C. At that temperature, there is a real risk of burns if you touch a radiator or pipe.

wbwrf

I'm looking at the options for replacing a 90s warm air "boiler".

- Modern condensing gas burner unit (no water) looks like ~4000 + fitting

- Aquair unit looks like ~2000 (to interface to separate standard combi gas boiler)

Condensing gas burner should be pretty efficient because it is working at input air temperature (20 degrees). Aquair needs hot water (say 60+ degrees, or 80 according to spec), which means combi boiler would be running inefficiently. Integrating Aquair with a heat pump system in future doesn't seem viable, as a heat pump can't work efficiently at 60-80 degrees.

So condensing gas burner looks best for now, although maintenance seems more costly. But if heat pumps are the future, what we really need is an air-to-air heat pump system that can handle the volume of air required by a central heating ducted warm air system. Does such a thing exist? 

Is my assessment more or less correct?

(I'm checking out possibilities for a house we're looking at buying, to budget for this.)