The general idea involves putting a bathroom extractor in the (originally external) wall between a sunroom and the main living space, and then using the extractor to import nice warm air (sunshine permitting) into the house.

The question is, what temp difference would be need between the two for transferred heat energy in the air to exceed the input of electrical energy?

One particular example fan (Vent-Axia Lo-Carbon VA100) can shift:

46m3/h (13 l/s) @ 2.5 Watts
or
84m3/h (23 l/s) @ 6.5 Watts

I'm sure there must be a formula...

PS. I suppose that the motor will be in the air flow, and thus its waste heat will be warming the air too, but that's perhaps gettnig a bit complicated?

Posted By: Seretthe air already in the rest of the house has to flow somewhere.

The house is certainly not airtight (I'm working on it, slowly...). I think the increased pressure would probably just up the leakage rate from the house in general?
Circulation would be ideal, of course.

In the absence of the fan, if we spot that the temp is looking favourable we simply open the (previously) front door and let the warmth ooze in. It works, but requires manual action and the effect is slow to reach the living areas. The effect could be improved by opening windows, but that's even more manual intervention so not done often. Overall the manual approach isn't best suited to grabbing a, say, 20 min blast of sunshine on an otherwise dull day. Hence thoughts of automation...

Unless your sunroom is really massive

~65m^3
But even so, I take you point. Maybe something less umphy than a bathroom extractor would be better suited to the task.

Unless it was under automatic control and could automatically switch off when the temperature delta dropped I think it'd be a case of overengineering.

If a fan were installed I'd expect it to have temperature based control of some sort.
I probably count as a fan (no pun intended) of overengineering...

Thanks for your thoughts.

Posted By: skyewrightIf a fan were installed I'd expect it to have temperature based control of some sort.
I probably count as a fan (no pun intended) of overengineering...

I would do it by using a temp comparator (and relay if req) to switch on the fan when the external temp (sun room) is greater than the internal house temp. Neil at reuk.co.uk made me one for my huge roof mounted extractor fan (for cooling my house), as follows:

"The final design is a fan controller which will turn on after 10 continuous seconds of the measured internal temperature being at least 1 degree hotter than the outside temperature. The fan will then switch off if/when the temperature difference between the inside and outside falls to zero or outside hotter for 10 continuous seconds."

All of the parameters were defined by me (with Neil's advice) and the board comes in a strong box with the temp sensors (you can order more cable if you want) - obviously you will want to reverse the on/off parameters! To me, what was amazing was that I got a consultancy service, a bespoke bit of kit and all for £29.99 based on this:

http://www.reuk.co.uk/buy-SOLAR-PUMP-CONTROLLER-WITH-RELAY.htm

Skyewright - this was my post on your other sunroom thread - as a fan of over engineering £30 will give you exactly what you want.

The house I'm in here is similar construction to Skyewright's - a solid stone croft house. My little solar warm air panel:

http://www.edavies.me.uk/2011/06/solar-thermal-box/
http://edavies.me.uk/2011/12/solar-thermal-end-of-term/

has been pretty helpful in drying the bathroom out during spring, summer and early autumn. The “control system” is that I open the window to it when I notice the sun is at all bright then close it around lunch time when the sun has gone off that wall. What it doesn't seem to have helped with much is warming the structure in the bathroom - the heat just doesn't soak into the walls and particularly the floor quickly enough to leave any noticeable warmth later in the day.

Posted By: Gotanewlife
http://www.reuk.co.uk/buy-SOLAR-PUMP-CONTROLLER-WITH-RELAY.htm

Skyewright - this was my post on your other sunroom thread - as a fan of over engineering £30 will give you exactly what you want.

Thanks for reminding me of that one. Your (their) comparator would do the trick nicely.

Posted By: joe90I found this very interesting on the subject of moving warm air into a house from solaroom:-

That was a large part of my inspiration too.
IIRC they just use thermosyphon circulation of the warm air (intake to upstairs, return from downstairs, both with computer controlled flaps).

Posted By: SteamyTeaNot enough energy to heat the thermal mass, that's interesting.

I don't know about not enough energy, as such. I didn't expect a single sunny morning to make much difference but did hope that the temperature of the thermal mass would come up slowly. However, I it seems that the connection between the air and the thermal mass is not sufficient to store much heat while the bathroom is warm.

This morning it's bright but cloudy after a dull start and about 16 °C outside, 11 or 12 °C in most of the downstairs, 22 °C in the ”manifold” of the warm air heater outside the window and 15 °C in the bathroom air yet a strip of tiled floor by the bath is still at 12 °C. It's so well connected to the concrete slab and the wet ground underneath that the warm air above and the insulating effect of the air/floor interface means that most of the available energy just ventilates through without stopping.

Posted By: Ed DaviesThis morning it's bright but cloudy after a dull start and about 16 °C outside, 11 or 12 °C in most of the downstairs, 22 °C in the ”manifold” of the warm air heater outside the window and 15 °C in the bathroom air yet a strip of tiled floor by the bath is still at 12 °C.

Our 'collector' is a bit bigger than yours...

Attached is (I hope) a chart showing a few temps for yesterday, plus the solar W/m^2, which shows that is was not a particularly sunny day (but massively better than Saturday, which peaked at 134W/m^2!). The cursor is positioned at 1030, which as you may tell from the 'F Hall' plot is when I opened the front door....

'Mid Hall' is the corridor that runs down the spine of the house.

PS. It looks as though the attachment worked - albeit that the image has been automatically resized (shrunk).

[Edit: PPS. 'Orangery' is the sunroom. The name was originally used in jest, and then stuck (but it's still a joke name, honest).]