Can someone explain why on earth some
shower controls turn up the cold water
100% - then - gradually start turning
up the hot water ???? (ie. you need to
twist them in one direction to first
get cold going, up to 100%, then it
starts to allow hot water to mix)....
This seems like a colossal waste of
water (since you're running the cold
valve wide open at max pressure) -
vs. the pull out type control where
you can control pressure & hot/cold
mix by pulling out for pressure and
twisting for mix).
Which brings us to HVAC systems - i've
seen building "environmental" controls
that run the AC continously - and when
a target temp is reached - instead of
turning off - they turn on the heater !!
WTF !???? wouldn't it make more sense to
just turn off the air conditioners ??
(instead of turning on the heater - while
the air conditioner is still running).
hell of a way to waste energy.
is there some thermodynamic reason behind
this (on the surface) idiotic logic ???
Don't know about the HVAC but for tubs & showers it is for safety.
Harder for kids to burn themselves if they have to turn past full cold
to get hot water. Most now have an adjustment also. I have theirs set
so that even if they turn it all the way to the left they can't get
New showerheads have a restrictor the limits the amount of flow to save
water. Kramer can get you one w/o the restrictor but it could cause
Safety? I don't know . . . It seems that a child, or someone like my
confused old mother, would panic on getting hit by the cold water and
quickly push the control around to full hot. And in a nursing home there is
no one who cares about stuff like hot water temperature. But at least it's
an excuse. It's the first I have heard.
I hate them. It's good to see I'm not alone! I had encountered them only
in hotels and assumed that was because they were cheap for some reason.
It was a disappointing surprise to find them in my new house! Joe
1. If a hot water recirculator is running, then the hot wter comes on
at nearly full temp within a very few seconds of turning the tap on
2. See reason #1, recirculators are becoming more popular and the
scald risk with 125F-135F water is real. Set you water heater for temps
lower than this and you risk bacterial infection from Legionnella (sp)
Commercial buildings are frequently run this way. Several reasons
1. Lots of people inside that dissipate heat and humidity to the building
2. Lots of equipment inside the conditioned space that generates heat
(computers, TVs, Lights)
Even with the need for heat, there is a significant need to dehumidify,
so the AC runs all the time.
The people and equipment do an admirable job of keeping the building at
or above the desired temp. When heat loss to the outside is low
(moderate weather conditions outside), AC load drops enough that heat is
AC gets sized for expected max occupants, max equipment thermal load,
heat gain/loss thru windows/walls and doors and for max outdoor temp.
If anything is less than max (people, equipment, heat gain from
outside), the AC loafs along, and may overcool the building. So add
heat to get the outlet temp back to spec.
Should be noted that these systems run the fans 100% of the time to
circulate air in all areas.
We did a multifamily building that very nearly had the AC situation you
If you are running a "blower" unit, you have your choice of a 2-pipe or
4-pipe system. 2-pipe systems are cheaper and the whole building runs
either hot or cold. So on a day when it's 50F in the morning and 80F
in the evening, you system is still running 1 or the other. So some
people are always uncomfortable, esp when one on the sunny side wants
AC and one on the shady side wants heat.
The 4 pipe system solves that problem by providing everyone with heat
and cooling and uses controls and fans to provide 1 or the other. Near
the set temp you should get neither. It should hold the room at about
the temp you set.
In our case, it wasn't really wasting heat or contributing to pollution
because both the heat and the cooling were on district loops. The heat
came from excess heat at a local power generation facility. The
cooling came from another industry. But if we didn't use it, it would
have been wasted into the air. So it really wasn't inefficient.
As for other buildings, so have quite complex systems that in mild
temperatures act like heat pumps. An AC doesn't magically create cold,
it removes heat from the air and blows the heat outside via the coil.
Some large buildings use the same concept. The run a system that
removes the heat from the air, puts it into one system to provide heat
to the building and uses the cold for the cooling loop. It then uses
supplimental heating and cooling when it gets beyond the limits of what
the system can handle.
You also have to remember that large buildings, unlike houses, have
"make up" air that gets introduced into the system so you get a certain
percentage of fresh air. Usually makeup air gets introduced in the
hallway. When you turn on the exhaust fan or whatever, the air goes
intot he unit for make up for what you are venting. The makeup air
needs to be heated/cooled as part of the buildings mechanicals. Often
these use heat exchangers to try to use some of the heat in the vent
air to pre-heat the incoming air.
Large buildings are very complex beasts. But they have good staffs and
consultants to make sure they aren't wasting money. So if they are
doing something, there's usually a reason for it.
Rare that people don't run the shower at 100%. One factor in the design is
safety. You get to temperature gradually. Water should be adjusted so that
it is not so hot that 100% hot will scald you. Many new shower controls
have safeguards for a maximum temperature. I'd bet there is realy very
little waste, if any, with that type of setup.
If it is a true environmental setup, it is not just controlling temperature.
Air has to be filtered and cleaned, humidified or dehumidified, depending of
the season and location. Your co-workers are farting all day long and
unless the air is freshened, you get to breathe their farts all day. It may
or may not be the AC running, but blowers bringing in fresh air as needed.
In large buildings, it is possible that some areas need heat at the same
time as others need cooking because of variables like sun load, people's
body heat, etc.
My first experience with a large AC system was in a printing plant. The AC
was not put in for the comfort of the workers, but for the control of the
air for the paper. It was often used to control humidity by running the
huge chillers and the boilers at the same time. Similar to the defrost cycle
on many automobiles that turn on the AC for a quick moisture removal.
Sounds dumb. If a house needs dehumidification, we might run an AC if
it also needs cooling or a dehumidifier if it also needs heating, but
what do we do if it needs neither? Maybe run both, but not for long.
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