NetNews Usenet Archive 1993 #1/NN_1993_1.iso/spool/sci/electron/22302

Internet Message Format | 1993-01-09 | 9.0 KB

Path: sparky!uunet!think.com!camb.com!bruce
From: [e-mail] (Barton F. Bruce)
Newsgroups: sci.electronics
Subject: Re: NEED SOLENOID ACTUATED WATER VALVE.....
Message-ID: <[e-mail]>
Date: 9 Jan 93 06:17:56 EDT
References: <[e-mail]>
Organization: Cambridge Computer Associates, Inc.
Lines: 159

In article <[e-mail]>, [e-mail] (Phil Biehl) writes:
> Hi. In examining my hydronic (hot water basboard) furnace, I find that
> it is divided up into three zones. What I'd like to do is put in
> electrically operated valves that controlled via a microcontroller and
> three separate thermostats, one for each zone. I need to find a source
> for these valves that will fit 7/8" copper piping. 12 Volt coils would
> be nice but not absolutely necessary.

Furnaces heat air, boilers heat water.

You say it is already in 3 zones. No seperate controls already?

Or is it just piped so adding controls would be easy?

Assorted bits of useful info follows in no particular order.

The circulator in a home heating is NOT a high pressure pump. You will
have only a few feet of head (pressures are so low feet of water are
used rather than pounds for any measurements - generally) across a
closed zone valve that you will NOT be able to reliably operate the
typical solenoid valve in that size range. Only tiny solenoid valves are
typically directly operated. Larger ones are all pilot operated. The
solenoid only dumps pressure from the top of a diaphragm that was
holding it shut. You will find that most hydronic zone valves are either
a bees wax and copper powder 'hydrolic fluid' pushed little piston with
a resistance heater cooking the fluid pot creating considerable
expansion (auto radiator thermostats are often a similar element heated
by the surrounding engine coolant), or are a small clock motor with
spring return.

The former type is typified by the classic Blue bonneted Dole valve also
OEMed by B&G with a red bonnet, or the Taco one or any of many others.

The best clock motor one that I like is by Erie, but is 'too good' for
the average -el cheapo- plumbing or heating supply house. It is
available in 24 volt and also in 120 and 240.

Many zone valves have a switch that is closed when the valve is opened.
This lets you have a simple thermostat to valve circuit and then all the
contacts in all the zone valves get paralled and any one closing starts
the burner and pump. If domestic hot water is also supplied from a
tankless heater, the controls will kill the pump if the boiler gets too
cold.

A zone valve can be in the supply or return, but last longer in the
return, as does the pump.

Often, to preclude any gravity circulation, a weighted check valve will
be put into each zone as it leaves the supply pipe leaving the boiler,
and the zone valve will be in the returns near the boiler.

Your 7/8" pipe is *called* 3/4" (trade size). Yes it is 7/8" od. Oil
burner size tubing, generally up to 3/8" OD is refered to by OD.
Refrigeration folks use OD all the way up to any size copper tube (2"
trade size to the plumber is 2 1/8 OD in referigeration).

Relatively LOW flow rates and designs for maybe 20 degree temp drop
typify such hydronic systems. High velocity water is noisy, costs LOTS
to pump, and the extra heat gleaned from your radiator or convector by
having a low temp drop end to end is minimal and you can get more heat
out simply having the water a few degrees hotter which it surely will
get as the minutes pass and the boiler keeps firing.

The actual port in a zone valve may be quite small compared to the 3/4
tubing - don't worry.

Lead hazzards prohibit traditional 50/50 (tin/lead) solder from potable
water piping. Better plumbers always used to use 95/5 (tin/antimony)
solder as it does not fail the way 50/50 will over the years on high
temp hydronic systems where the temperature cycles way up and down many
times a day. 95/5 doesn't wet out as nicely and you need a very clean
joint and good flux and proper soldering skils.

Some of the now popular 'Bright' or 'Silver' solders plumbers only
recently are having to afford are VERY good, wet well and flow VERY well and
are ~ 4 times as strong as old 50/50. Refrigeration types have for years
used these low temp silver solders (only a SMALL amount of silver is
present) and the most popular was probably Harris's "Stay-Bright" a
eutectic alloy, or "Stay-Bright 8" one with a tad more silver and not
eutectic. The latter's short plastic range is useful in poor fitting or
LARGE size joints where the regular stuff almost pours out. These are
excelent for hydronic systems.

Any plumbing supply house has some brand of these valves. Unless you
speak and look like a tradesman, expect to be reamed for list price.
Better find some place like a Home-Depot. I think there is a
HOMEDEPOT.COM - try whois with possible spellings.

Better valves like the Erie ones probably WON't be at H/D. If you can
get Erie ones, they have ONE SIZE BODY and adapt to your pipe with
provided adapters. Erie is a very professional valve and has orifice
size options that you can ignore in your application. These different
orifice sizes have corresponding different CVs (gals/min at 1 psi
pressure drop through valve). In your application ANY of their standard
CV ratings is ok. Some higher pressure commercial system CAN'T use the
larger sizes because they won't close/open properly against the higher
head with the larger area port. Other 'plumber' grade zone valves won't
even offer different CVs/orifice sizes.

FWIW a pneumatically operated zone valve will typically have several
optional CVs *and* will have a carefully contoured modulating
characteristic and will seldom need to be fully open or closed when in
operation. That class hardware is WAY beyond home systems needs.

The nice thing about the Eries (and some others) is that without
disassembling or careful FAST soldering you still have no danger to the
valve. They have sweat (the solder joint) to inverted flare adapters you
can install first and when cooled the valve gets installed with a
wrench. This also lets one valve body with one inverted flare size be
adapted to ALL reasonable tubing sizes. Only the adapters differ as you
buy valves for different pipe size. OTOH, the 3/4 you are looking for is
VERY common and may be the ONLY size many smaller stores carry.

Zone valves should be cheap, but are not. Some small circulators are
water lubricated. The rotor is INSIDE a non-magnetic stainless shell and
the coils are all outside. The pump has no moving seal problems.
Curiously, many of these don't cost that much more than a zone valve,
and often the weighted check ('flow control valve') will again be at the
supply end of each zone and the pump at the return. No zone valve at
all! NB that in this config you MUST have that check because without it
you may get REVERSE flow in 'off' zones induced by pressure from pumps
in 'on' zones. You also will need a control relay as the pump is 120v
and 24 volt thermostats always make more sense than 110v ones (except in
electric heating situations - which NEVER themselves make any $ sense
at least in cold climates).

The time constants in home heating are very long, and nothing has to
happen instantly as far as just keeping the place warm is concerned.
Valves can open slowly, and the pump(s) and be killed to protect hot
water during showers, and noone notices.

More sophisticated control may come from not simply cycling zone valves
based on room thermostats, but from resetting boiler temperature based
on outside temperature (possibly adjusted for wind chill). The Zones
will be circulating more constantly, but you will have evener heat. A
small resistor artificially warming your outside sensor slightly will be
negated by rising wind. In general on your type system, a 1:1 reset is
ok. Start at 140 degree water at 60 out and jack water temp one degree
for each degree drop outside. You may need to tune this slightly.
Remember that home hydronic systems may well be designed to EXCEED
normal boiling point on the coldest days and won't boil and make
pounding sound as the steam bubbles collapse because the system is
pressurised and boiling point is higher than 212. Burner gets cycled to
keep water near desired temp, zone valves open on thermostat demand, but
'on' cycle will be quite long - that is what you want.

That simple system is no go with boiler heated domestic tap water. In
that case there are MANY schemes, but an Erie 3 way valve can be cycled
to take boiler water or bypass the boiler to average to the desider temp.
This one valve would be in addition to other zone valves/pumps and
serves them all. There are many other schemes using restrictions with
regular 2 port valves to avoid 3 way ones. One flow path is through
restriction (possibly bypassing boiler) second path is through boiler
via valve. Water WILL circulate in zone in either case. valve open, MOST
goes through valve and boiler, little through bypass. Valve closed, all
must bypass. Venturi Tees (aka MonoFlow Tees), and primary/secondary
pumping schemes can all be used, too. See any library.

Well there is lots more, but this really isn't rec.plumbing