Hot water to heat the house is going to give you a lot of penalties. No wonder you didnt judge it worthwhile. There are freezing issues, plumbing, heat exchanger if using antifreeze, and output temp too low to be genuinely compatible with existing CH systems... and at the end of it efficiency of such systems is low anyway.
What would be the sticking point with hot air heating? It'd be way less work, some common issues are workroundable, and cost and payback are both much better than hydronic.
However, as I've got drastically oversized radiators, due to the upgraded insulation - it's not quite as bad as that.
No, there is no way that it'll hit normal CH temps.
40C in much weather should be quite achievable, and give a pretty good temperature boost.
Freezing is of course an issue - in my case this is likely to be dealt with by simply using a frost stat, to heat up the radiator a tad.
Noise. Filtering. Power consumption of fans. Large ducts through awkward spaces. Very hard to store heat. Valves are more awkward. Insulation of ducts is much, much harder.
If I had a warm roof, then I'd certainly be going for heated air.
yes, but each time your CH comes on it knocks the solar gain out. Unless you've got a system where you can set the circulating water temp to modulate to the minimum needed to achieve the right heating temp at any time.
OTOH DG panels should perform better with CH, which is really whats wanted for year round use.
Right. One more complication though. Not sure how the pump plus frost heater power consumption compares to the optional low speed fan for hot air.
There are silent low speed fans, though not many are designed for that. Noise is most easily dealt with by using a passive system, no fan at all. Power consumption is then zero.
The easiest & highest % ROI way to address ducts is to have none, and only heat 1 side of the house directly. The other side gets partial heat from the temp difference mentioned below. You then have no ducting insulation either. This works if your CH can cope with the differing heat output requirement, ie has some form of room stats.
Heat storage, again its easier not to for maximum ROI %. If you want the place heated in the day this works fine. There is some evening heat storage in practice, because you can set the solar stat to above the CH stat. IOW your solar heats the house to the upper end of what you decide is comfortable, and after sundown this temp slowly falls for a while until CH needs to come on. This avoids the evening warm up plus some ongoing heating.
If by valves you mean to prevent night time cooling, a plastic film damper closes when theres no panel airflow in the desired directoin. This thin damper will lose a bit of heat at night, but the daytime gain well outweighs that.
If you mean for automatic thermostatic control, a servo plus light hinged rigid damper will work. polystyrene would approx eliminate the small night time heat loss. Yes its a bit harder than switching a pump off, but much easier than the complications of a hydronic system.
The ducting details above assume your panels are at ground & maybe first floor level. If they're on the roof, a single duct down the corner of a room would suffice for some types of layout. Air returns upward through the living spaces, with a grille & wrapped duct for the attic. Only the attic duct needs any insulation.
For a fanned roof mouted system, a noise filtering labyrinth at the top can make the system virtually silent. DG panels support much higher working output temp, which works with less air flow. Having used a labyrinth for a job here I've been impressed with them, very effective.
If you want to avoid a periodic clean, vehicle air filters are cheap and readily available.
Systems that heat less than all the house all the time are always open to extension in future if desired. Flat panels perform ok in overcast conditions, and can be located away from the house if need be. Mesh absorbers give very good efficiency figures.
on slightly, assuming I decide on a comfort level of 21C and wish to calculate the rate of return on my investment in insulation, what is the figure I should use for the average temperature difference between inside and outside. I imagine its units are degree days but what is the average for SE England?
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