Alright guys, I could do with the help of some you clever people here.

For one of my college assignments, I had to design 2 heating systems
right from the beginning; working out U-values, heat loss calculations,
selecting emitters, sizing emitters, pipe sizing etc.

I've been pretty successful with this however, when selecting the boiler
I need to analyse how closely it matches the requirement. Therein lies
my problem; I have designed my system on a DeltaT of 30 (60/40/20), the
boiler I have selected (Vaillant Ecotec 618) states outputs for:

80/60: 3.8 - 18.5kw

50/30: 4.2 - 19.3kw

My requirement is 18.5kw at 60/40, is there any way to work out what
kind of output the boiler would produce at this flow/return temperature?
Also, on another note, the heat input is stated as 18.6w..so when it is
working at 50/30, it is over 100% efficient?!

--
David

On Mar 31, 5:59*pm, gremlin_95 wrote:
Alright guys, I could do with the help of some you clever people here.

For one of my college assignments, I had to design 2 heating systems
right from the beginning; working out U-values, heat loss calculations,
selecting emitters, sizing emitters, pipe sizing etc.

I've been pretty successful with this however, when selecting the boiler
I need to analyse how closely it matches the requirement. Therein lies
my problem; I have designed my system on a DeltaT of 30 (60/40/20), the
boiler I have selected (Vaillant Ecotec 618) states outputs for:

80/60: 3.8 - 18.5kw

50/30: 4.2 - 19.3kw

My requirement is 18.5kw at 60/40, is there any way to work out what
kind of output the boiler would produce at this flow/return temperature?
Also, on another note, the heat input is stated as 18.6w..so when it is
working at 50/30, it is over 100% efficient?!

--
David

The best way to come to an approximation is to draw out a graph an
draw a line to joint the dots and project the line
The result is non linear so exactitudes are not possble by simple
ratios.
As for the 100%+ thing, there are two possible reasons one is it's non
liear. and the other is the traditional way od expressing heat outputs
from boilers.

In days of yore when boilers were inefficient, no account was made of
the latent heat of water in the flue gas.
However now we have condensing boilers, this latent heat is now and
issue.
It's down to what is called net and gross calorific values of the
fuel.
Manufacturers like to use the net value, it makes their boilers look
more efficient on paper.
A sales ploy.
So some condensing boilers, using this value have 100%+ efficiencies
due to the latent heat recovered by condensing the flue water vapour

Read up here on the topic.
http://en.wikipedia.org/wiki/Heat_of...#Heating_value

It's called higher and lower heating values here, probably written up
by some Yank.
Same thing, different terminology.

In article ,
gremlin_95 writes:
Alright guys, I could do with the help of some you clever people here.

For one of my college assignments, I had to design 2 heating systems
right from the beginning; working out U-values, heat loss calculations,
selecting emitters, sizing emitters, pipe sizing etc.

I've been pretty successful with this however, when selecting the boiler
I need to analyse how closely it matches the requirement. Therein lies
my problem; I have designed my system on a DeltaT of 30 (60/40/20), the
boiler I have selected (Vaillant Ecotec 618) states outputs for:

80/60: 3.8 - 18.5kw

50/30: 4.2 - 19.3kw

My requirement is 18.5kw at 60/40, is there any way to work out what

Have you allowed extra so the system can heat the house from cold?
Providing what's required for just the steady state losses when up
to temperature means it will take an unacceptably long time to get
up to temperature in the first place. What you could do is run the
system at 70/50 to provide fast warmup from cold, which would require
an extra 1/3rd power input, e.g. a 24 or 25kW boiler.

Also, when the outside temperature is below your design temp (typically
-3C for condensing boiler systems), you'll need more power to hold the
inside at 20C.

kind of output the boiler would produce at this flow/return temperature?
Also, on another note, the heat input is stated as 18.6w..so when it is
working at 50/30, it is over 100% efficient?!

100% efficient is max possible efficiency for a non-condensing boiler,
so yes, a condensing boiler can be over 100% efficient against this
baseline. If you invented a solidifying boiler (dropped the condensate
out as ice cubes), you might achieve even higher efficiency if you had
invented a way to get the extra latent heat to the boiler output.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]