How Does This Old Fan Convector Work? (w. Diagrams)

D107

The photo below is of a 1970s era Selectronic Mark 9 Series A-9 fan-assisted convector that in its day provided both heating and AC with it's own compressor built in. Now it just does heat. The black knob clearly shows the direction of more or less heat. Its white dot would indicate a relative temperature setting, however I'm not sure if the higher black numbers indicate more heat--since if you keep going counterclockwise, the numbers eventually go down. The outer ring I'm not understanding at all (with the white band 3/4 way around). Was that for the AC only? The fan is internal thermostat operated I believe. Anyone recognize this?

D107

I'm reposting this thread to see if anyone can decipher how this works. I ask because now that house is being sold, engineer came by and inspected the unit and moved the dial to heat maximum. I came back the next morning and found the fan on apparently giving some warm air flow--or it could have been the sun on the rad-- yet the boiler had not been on. So for the first time I'm thinking this has some kind of electrical element in it that creates heat if the dial is set to higher heat level. Which would confuse me no end--how would they integrate hot boiler water into this. I always assumed this was a kind of hydro air where the fan would come on when the was boiler was circulating.....

GBart

Done, over, 50 years old, time for new, nice museum piece, what engineer came in????

Your HVAC contractor should be able to explain it, without total photos this has little meaning.

D107

@GBart
Thanks; the buyer's home inspection engineer came in. If I was going to live there I'd put in a nice panel rad...but we just want to make sure it's working property as per contract....attached are notes and diagrams from the brochure. The AC part of this has been disconnected. Unfortunately fan seems to run even when boiler is off. Perhaps we have to disconnect fan operation and make it pure convector. Electric bills were not that high, but perhaps fan is unnecessary. Hopefully attached diagrams will help.

Solid_Fuel_Man

Wow, that is a really neat idea! I wonder why it never took off?

Using the heating water also as the waste heat for A/C. It's really an ingenious idea!

Also note on the "Typical Simple System" diagram they are pumping away!

Solid_Fuel_Man

It looks like there is a "reverse acting" aquastat, I'd think a simple snap-on type switch could be wired in series with the fan to only operate when there is a call for heat. Too bad the refrigeration is gone, I'm still fascinated with this idea!

D107

@Solid_Fuel_Man Thanks for your note. I have to laugh since my late father, an HVAC engineer, got four of these units for free in the late 1960s. My mother hated them since the outside sprinkling system always had to be turned on to dump the heat. I think my father enjoyed the experiment. With your switch idea, I'm guessing you'd have to run the line for that snap-on switch all the way back to the boiler or taco relay; and there's still two other units like that in the upstairs bedrooms. The simple solution is to turn the unit's t-stat dial all the way down, so that the fan never comes on. The unit will still heat, though it won't put out as much. I see from the tables that the unit, at 215º puts out 17K btu, so with this Buderus G115/21 and outdoor reset on a cold day at 160º probably puts out half that, which is likely enough for the room. This 50 year old unit is not something we're looking to put money into as we sell the house--just want to make sure it's working reasonably. If we set the Logamatic for a water temperature that brings the house to a target temp just below what zone thermostat is set for, then we would have defacto constant circulation and so in that case the fan wouldn't be wasted as it pushes out the residual heat.

Solid_Fuel_Man

If it will heat without the fan then what you are saying will work. Just natural convection if your current water temps are adaquite for these units to have enough output to heat the room.

D107

Yes, alternately I could lower the fan-t-stat-dial until it doesn't come on so often or by itself. I think that's what was going on in practice all along. When the engineer came in he really didn't know the history of this thing, so he jacked up dial all the way. Also, since there's no more AC, the 'summer -winter' toggle can probably just be left on Winter all year round. The downside of this sytem would be that you have to water your lawn whenever the ac comes on, which could end up using a lot of water = $.

ratio

Neat! It's the Grand Uncle of a modern water source heat pump, only it uses the tube-in-tube(-in-fins) heat exchanger as the heating element directly, thus the compressor provides cooling only. The sequence of operation is sound—there are any number of high-rise buildings using WSHPs to move heat in & out of a hydronic loop that is maintained via boilers & chillers as the season determines.

If the tube-in-tube-in-fins HX is undamaged, it should be possible for a skilled AC guy who likes to tinker to get it working 100% again.

D107

I see from the patent number it was invented in 1960. Maybe i'll post the diagrams. The family went to central ac later on so these units had the cooling de-activated.