Subject: Recommendations for HVAC programmable controllers?

From: [email-masked] (James VanBokkelen)
Date: 18 Oct 1995 23:21:07 -0400

Anybody using programmable controllers in HVAC applications?  I know
most installations use relay logic & maybe timers, but sometimes things
must get too complicated...

I am dissatisfied with current commercial solar hot water differential
controllers; to replace them I need something that can monitor 3
temperature sensors and drive at least 1 relay (3 would be better) to
control 110VAC devices.  The development system should run on an
IBM-compatible PC, and I'd rather not buy or borrow a PROM burner.  I
can cope with whatever machine language the micro uses as long as I
can get a manual.  24VAC powered would be nice, but I can cope with
110VAC or 12VDC.  Low power consumption is a plus, as is an enclosure
I can buy rather than fabricate my own.  UL listing not necessary, but
nice.  RFI emissions suitable for home use (e.g. low) another plus.
I'd pay extra for a 2-4 character 7-segment display & 1-8 membrane
keys on the front, particularly if I didn't have to write my own
drivers for them.

-- 
James B. VanBokkelen					Far Acres Farm
Address known to work: "[email-masked]"		South Hampton, NH

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From: [email-masked] (Nick Pine)
Date: 19 Oct 1995 04:17:22 -0400

James VanBokkelen <[email-masked]> wrote:

>Anybody using programmable controllers in HVAC applications?
... 
>control 110VAC devices.

I suppose you know about the Heliotrope General Temptrak II, about $180
wholesale, which takes up to 5 thermistor temp probes and has a 3 digit
display and a 110 VAC receptacle on the box.

The Lambert Engineering Data Trap costs $2,500 and uses 6 watts, with AD592
temp probes. It has 8 analog input channels, 8 digital inputs and 8 digital
outputs (which need relays to drive 110V, eg the nice 2.5 A Crydom D1202
solid state relays available used for $3.50 each from All Electronics at
(800) 826-5432), and this is expandable. The Trap does a good job of measuring
AC single or polyphase power with current transformers, even for devices
with odd current waveforms. We attached a LiCor pyranometer to measure sun
power. It has numerous programmable algorithms to control output channels, an
RS-232 interface that you can attach to a modem, etc. There are cheaper data 
logger/controllers around, if you don't need accurate AC power measurement. 

Have you checked out MicroMint controllers?

Nick