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40 minutes ago, JSHarris said:

The biggest single difference between dyno readings I used to see on my old hillclimb/sprint cars was down to variations from one dyno to another (these could easily be around 5% to 10% alone).  The next greatest variation was from temperature density, as even with the dyno fan running flat out the air temperature at the intake would vary in line with the weather and with how many runs had been done that day. 

absolutly agree ,

but that in most cases is down  to the operator not setting it up correctly  or no baro /air temp correction in the software for the dyno, or not running on light load for enough time to warm up dif+g/box.and many dynos have very poor cooling fans 

and of course if you were on carbs ,not injection difference would be very noticable ,as no corrections for air +baro  possible    .std fan that they supplied with dynos were always only meant for quick run up not constant load for mapping  an ecu  in 256 spots

to get repeatable results you need to keep everything the same as is humanly possible .

 

i built mine more  as a poor mans  test cell with  7.5Kw 3phase  furnace fan sat in front of car as well as cooling extractor fans on dyno retarder unit  as well as another air extract fan for the whole cell +exhaust extract .

there is a lot of heat in a dyno cell  to get rid of 

you would not want to stand outside the car for long with a 60mph wind from furnace fan 

It was done So I could acurately check the mods we made to our own race car were actually an improvement ,running 1300c class -every bhp was worth the work to find it 

result 3 years in a row we won the scottish saloon car championship and 2 years the scottish sprint championship  with our  citreon 1294cc AX sport and also won our class  in the 6 hour birkett relay race with 2 other  ax,s at snetterton  

I did this very early on as i found you could not do continuous mapping because of the air temp and engine water temps rocketing and making a nonsense of the map you were writing even with air temp and baro corrections   if it was injection 

early days you had to write ,then burn a chip -then carry on --

which is also why on most maps only a small portion was actually mapped rest was entered manually . for club race cars  etc most did not need or want to pay for a full map 

but for road use then you have a lot more work to do 

the advent of cheap wide band lambda sensors etc and ecus that you could write directly too changed it for the better ,then  being able to enter target lambda maps made it even easier . as you could drive it on rollers -then download the corrections the lambda had logged for partial throttle settings ,then not much time spent for WOT mapping --lot easier on the engine as well

 

 

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Getting back to the original topic, I too don't think a thick slab is all that necessary and may sometimes be harmful. In general, I don't think living too close to the thermal store is a good idea. This is a generalization of concerns that Earthship-style designs are not likely to work too well for houses with significant temperature swings with longer than diurnal periods. E.g., the Hockerton houses get cooler than I would be happy with in the winter. Presumably this could be fixed by harvesting more heat in the summer and autumn but the cost of that would be having the houses hotter than would probably be comfortable.

 

A thick slab seems to do three things:

 

1) provide structure so that localized loads are spread over the insulation below,

 

2) act as a heat store so that timed heat sources (e.g., solar or E7) can be used 24 hours.

 

3) act as a buffer to moderate the room temperature.

 

I don't know about (1). I've previously suggested CLT for this but nobody seemed much interested. Whatever, it seems to me there's better ways that don't involve so much embodied emissions.

 

The problem with the slab as a heat store is that there's very little temperature variation which can be tolerated so the usable heat capacity is quite small. This is because there's no control of the way heat comes out of the store.

 

So we're left with it acting as a buffer to moderate room temperature. That's an awful lot of concrete to use to avoid a relatively simple control problem.

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