Grundfos claim that their "autoadapt" DHW circulation pumps "learn" hot
water usage over a few weeks and switch on/off accordingly. I don't
think that our usage follows any particular pattern so I'm wondering how
it will respond.
Has anyone here installed and used one?
Ah the old artificial intelligence again. What was it Monty python said? If
there is such a thing as artificial intelligence it has to be a good thing
as there is bugger all of it on the Earth.
Trouble is, its us humans wot make these so called artificial intelligences
in the first place.
One of the most annoying is those which try to predict what you are typing
all the time.
What is your query?
Did you mean pubic transport?
This newsgroup posting comes to you directly from...
No it’s not. It’s circulation of hot water from the tank around the whole
hot water system and back to the tank (in order to provide near “instant”
hot water from any hot tap). Common in hotels, rare in domestic
To keep the pipe filled with hot water would only require a very slow circulation rate.
Therefore the return pipe from the furthermost tap could be very small bore, say 10mm.
Less heat loss from a small pipe too.
Well yes, the lower the heat loss in the recirculation circuit, the the smaller the
recirculation flow-rate needed. Thinking further, perhaps sufficient flow rate could be
achieved by thermal circulation, e.g. by wrapping heater tape around the lower part of the
return pipe. Might only need a metre or so warmed up to a few degrees above the delivery
On Sunday, 23 September 2018 19:19:52 UTC+1, Phil Addison wrote:
rate could be
lower part of the
ve the delivery
The return leg needs to stay at at least 60 for legionella risk. What you d
escribe has nowhere near the temp rise or bore of old gravity backboiler HW
systems, so I'd expect close to zero circulation. Even slow gravity circul
ation would significantly raise the temp at which the HW would need to be d
elivered to the pipe run.
On Sun, 23 Sep 2018 12:30:02 -0700 (PDT), email@example.com wrote:
In the system I describe the return water is heated just after the final tap and since the
whole point of recirculation is to maintain full delivery temperature to the tap/s, it
follows that the water in the return pipe is hotter than the DHW delivery, which should
have been designed to kill legionella.
Err, I did say "a few degrees" and "10mm". We are not trying to heat the whole DHW tank;
that's already been done.
We are talking of only the few litres (maybe 10-15 max) in the leg to the furthest tap,
plus a fraction of that in the small-bore recirculation pipe. Heat loss from (X) metres of
lagged 15mm pipe (or whatever size it is) equals the required wattage of heater tape round
the 10mm pipe. The heat loss also enables to you to calculate the temperature drop, tank
to tap. Knowing the water density at these two temperatures you will know the circulation
head available. Now you just need to work out the pipe friction to see if the head exceeds
the friction. If it does you get circulation; if not you can increase the bore of the
recirculation pipe and/or put more heat into the tape. The excess will be absorbed in the
tank which will be compensated by the boiler shutting off a little sooner.
I think there is a good chance this would work. Someone just needs to do the sums to say
yay or nay.
It might -- however: the circulation does increase the heat losses, lagging or
no. The circulation pump can be shut off, more difficult to do with a gravity
These systems are fairly common in Treznal, where the mandated legionella
testing for larger sharer DHW systems. Usually, it's lagged pipe out, 10mm
lagged back, because it's less loss per meter, easier to route and easier to
lag. Gravity tends to need serious diameters, and it's harder to get the entire
pipe system hot using gravity. This can be a concern because testing is
relatively expensive, and any savings by using a gravity system will me lost
many times over if legionella are found, and a retest is necessary. (The system
is cleaned by running it at 65°C or so, while circulating, and flushing all legs
to get the pipes to the water temperature.) The pump is usually on a simple
timer to shut off the circulation when not needed, to reduce heat losses when it
has no use. Fancier heaters include the timer, and fire up the circulation once
weekly in the early a.m. as part of a routine "heat everything" disinfecting...
There are a lot of more-or-less homebrew control systems for the pump: one
assumes you open the hot tap for a moment, and takes that as a signal to fire up
the pump, detection by two temperature sensor along the hot water "out" pipe. Or
a radio-linked button one presses to call for hot water. Or microprocessor
control of the hot water return temp, via pump speed. Or track usage with
varying ingenuity, i.e. accounting for weekdays, holidays, etc.
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