RE: Intelligent AC motor control

["Nigel Giddings" <nigel@xxxxxxxxxxxxxx>]

David,



I have just fitted a MVHR box from Greenwoods. A very basic model that
uses two AC motors. It is wired with a transformer on the extract side
so that you can vary the 'Normal' setting by changing the Transformer
taps or have a 'Boost' setting which is basically flat out.



At the moment it is wired permanently to the normal setting. I was going
to use a change over relay to switch between Normal and Boost, they
supply a 2 way switch for this but its not very HA.



I not sure how much control you need. It would seem two settings are
adequate here. It is only background ventilation anyway. The boost may
be useful in the depths of winter during the day with a full house and
the windows closed, at the moment I only have about 6 weeks experience
and most of that is negated by solar gain from the windows and people
opening windows. Rooms that are kept closed for 24 hours plus do settle
at a comfortable level, especially the basement cinema room. The Games
room is being over heated by the boiler / heatstore at the moment and
Node 0 is probably hot enough to make bread in....



HTH



Nigel



-----Original Message-----
From: David Chapman [mailto:david@xxxxxxx]
Sent: 08 August 2007 16:36
To: ukha_d@xxxxxxx
Subject: [ukha_d] Intelligent AC motor control



Automated Home DiscussionI'm sure someone here will know the answer to
this.

I'm setting up a whole house heat recovery unit. This uses two radial AC
fans, each 240v 90w. One basically pushes air in to the house and one
pushes air out, both via a heat exchanger.

If I run them flat out all is fine, The power factor stays around 1 and
together they use about 180w. But I want to run them at reduced speed
for three reasons, I don't need the air flow rates all the time, I want
to reduce noise and of course want to reduce power consumption.

The system came with a fan speed controller but it's old technology
(looks 1980s) and when I measure what it's doing although it reduces
speed and noise the fans seem to use almost the same quantity of
electricity, it appears to change the power factor which I recall isn't
good.

I'm sure I've seen devices that reduce the speed AND power consumption
of AC fans / motors but I've been unable to find anything. Any ideas
anyone ?

David C

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