Engineering Notes 1

H/Motel Spigots and Faucets

Generally, for a sink, shower or other wet area that requires water of varying temperatures one will install either two spigots mixing into a single faucet or a single "mixer" spigot and one faucet (these last two may be integrated). I'm ignoring the older style of two spigots and two faucets.

These two setups allow control of two oupts via two control inputs. Either:

1. Temperature (T) and Flow (f) via Hot flow (H) and Cold Flow (C)
2. Temperature (T) and Flow (f) via Hot/Cold Ratio (r) and Flow (f)

However many motels here seem to have gone a different route - simplify things for the guest by denying a variable, aka a mixer spigot with only one axis of rotation (off, then rotation from cold to hot). Indulge me in my MatLab presentation. Let's assume the hot source is 80degC and the cold 10degC. This leads to:
oneT=(10C+80H)/(H+C)
onef=H+C
twoT=70r+10
twof=f
Normalising all input variables to the range [0,1] we can create the following:

Or as contours:

In any case, the bottom line is the hotel picks the flow (and it's generally pretty high, I prefer falling water over jets) and you don't get that "spiral staircase" (see contour) temperature discontinuity as you would with traditional home-brew water management

Jump for code...

syms H C r f
oneT=(H*80+C*10)/(H+C);
onef=H+C;
twoT=r*70+10;
twof=f;

values=linspace(0,1,21);for

xvals(i,j)=values(j);
yvals(i,j)=values(i);

endi=1:21for j=1:21endC=xvals;
H=yvals;
r=yvals;
f=xvals;
oneTeval=eval(oneT);
onefeval=eval(onef);
twoTeval=eval(twoT);
twofeval=eval(twof);

subplot(2,2,1);
contour(oneTeval);
xlabel(
ylabel(
title(

subplot(2,2,2);
contour(twoTeval);
xlabel(
ylabel(
title(

subplot(2,2,3);
contour(onefeval);
xlabel(
ylabel(
title(

subplot(2,2,4);
contour(twofeval);
xlabel(
ylabel(
title('Cold Flow');'Hot Flow');'Temp vs H,C');'Flow');'Hot Ratio');'Temp vs f,r');'Cold Flow');'Hot Flow');'Flow vs H,C');'Flow');'Hot Ratio');'Flow vs f,r');