... allowing the water to enter the rad quicker than it is leaving. ..
presumably only until they burst?
... allowing the water to enter the rad quicker than it is leaving. ..
You get more resistance moving fluid in a vertical direction than you do moving fluid in a horizontal direction. There is more “internal” fluid loss when pumping vertically than horizontally. Additionally there is more loss when moving fluid upwards than downwards.
In a nutshell what I’m saying is if you had a 100m length of pipe, the frictional losses are the same irrespective of orientation. But if the pipe is mounted vertically the Total losses (frictional + internal fluid) will be greater vertically than horizontally. This is completely different from head but still related to “head loss”. .
I took the liberty of phoning up grundfos today and spoke to a guy in the tech dept. He said if the total resistance of the system was greater than approximately 150kPa, the pump would self circulate. He went on to say that this corresponds to a height of about 12m, beyond that the pump won’t pump as the resistance would be greater than 150kPa just in internal fluid and friction losses.
The actual process involves the shape of the rooms, which way the room faces convection currents, position of furniture, temperature against time, predicting when the TRV’s would click off etc. Thus its not possible to actually say that my rads are emitting X kW of heat. This might have sounded OTT but I got fed up of having a heating system that would work in the steady state scenario but in order to get to the steady state would take 3 hours. I’ve only got half my house done but my aim was to get the house up from 10C to 22C in 15 minutes with a temperature outside of 1C. This is largely helped because of the parameters on my weather compensating boiler which increase the flow temperature for a predetermined period before backing off.
When I did my heating calcs I opted to increase the size of my rads by 50-100%
sanj wrote
When I did my heating calcs I opted to increase the size of my rads by 50-100%
Don't you think that was OTT considering you have WC ?.
Why do you consider the pressure losses through your oversized radiators to be significant ?.
And just how much pressure drop difference is their between say a small ( K1 type) 438mm and a 2165mm (Length) assuming heights are the same ,lets say 530mm. (Myson).
I would just also point out that a number of people doubted I was telling the truth when I said the pressure loss on a reducer was greater in one direction than another. Nobody believed me that time either.
Can't imagine why they would, it's perfectly standard stuff.I would just also point out that a number of people doubted I was telling the truth when I said the pressure loss on a reducer was greater in one direction than another. Nobody believed me that time either.
Completely INVALID analogy! When you're diving, you don't have water INSIDE your lungs to help you push your chest out!Bit of a bad analogy but if you are diving, there will come a certain depth where you can no longer breathe without a pressurized supply. The same thing happens with the pump. If the column of water is too big - it won't pump.
D Hailsham, I designed my heating system for a transient state not a steady state, So when I said I doubled my rad size, this was a bit of a simplification. The actual process involves the shape of the rooms, which way the room faces convection currents, position of furniture, temperature against time, predicting when the TRV’s would click off etc. Thus its not possible to actually say that my rads are emitting X kW of heat.
You also said that you were using 50°C flow and 30°C return. This means that the mean water temperature is 40°C and, assuming a room temp of 20°C, the differential temperature between radiator and room will be 20°C.sanj.varah said:I did point out that I had circa 40kW (@80C flow, 60C return) of rads hooked up to my boiler
D Hailsham, I designed my heating system for a transient state not a steady state, So when I said I doubled my rad size, this was a bit of a simplification. The actual process involves the shape of the rooms, which way the room faces convection currents, position of furniture, temperature against time, predicting when the TRV’s would click off etc. Thus its not possible to actually say that my rads are emitting X kW of heat.
What I wrote has nothing to do with transient or static states and I did not say that you rads are emitting X kW of heat.
You said the following:
You also said that you were using 50°C flow and 30°C return. This means that the mean water temperature is 40°C and, assuming a room temp of 20°C, the differential temperature between radiator and room will be 20°C.sanj.varah said:I did point out that I had circa 40kW (@80C flow, 60C return) of rads hooked up to my boiler
If you look in any radiator catalogue, you will find a table which shows the factor by which the radiator output must be multiplied if the differential is not 50°C. In your case the differential is 20°C, so the factor is 0.304. A radiator which delivers 1kW with a differential of 50°C will only produce 304 watts if the differential is 20°C. Radiators which produce 40kW will only produce 12.16kW.
Are you actually saying that, while the house is warming up, the boiler will be running at 80°C/60°C - i.e the rads will be delivering their advertised out put; but, when the room is up to temperature, the boiler will automatically throttle back to 50°C/30°C to maintain the room temperature?
Sanj wrote
I would just also point out that a number of people doubted I was telling the truth when I said the pressure loss on a reducer was greater in one direction than another. Nobody believed me that time either.
You never answered my final point on that thread about velocity and the wide variations between the two sets of tables.
Sometimes I don't know why I bother, onetap you are clearly on a higher plain than me and I'm going to let you feel all high and proud..
OneTap, As regards to my heating calcs. Its part of some research I do so once the paper is published you can decide if you think its utter twaddle or not.
Sanj wrote
I would just also point out that a number of people doubted I was telling the truth when I said the pressure loss on a reducer was greater in one direction than another. Nobody believed me that time either.
You never answered my final point on that thread about velocity and the wide variations between the two sets of tables.
what was the question again or do you have a link?
Sanj wrote
I would just also point out that a number of people doubted I was telling the truth when I said the pressure loss on a reducer was greater in one direction than another. Nobody believed me that time either.
You never answered my final point on that thread about velocity and the wide variations between the two sets of tables.
what was the question again or do you have a link?
//www.diynot.com/forums/viewtopic.php?t=101309&postdays=0&postorder=asc&start=60[/QUOTE]
I can get to the iklimet table but the table referenced on photobucket is coming up blank for me.
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