The "mini split" type heat pumps and AC units that I have installed in
my house have a single outside unit and multiple (2) inside units.
The inside units have a finned coil and a fan. The outside units have a
finned coil, fan, compressor, and the control electronics. (They have
variable frequency drives running _everything_.) The inside units
typically mount near the ceiling on the wall.
Here is a link with pictures of a typical installation:
https://www.bobvila.com/articles/mini-splits/#.Wh-azHlrxpg
The ones with a high SEER rating are _unbelievably_ quiet. Less noise
that a refrigerator. We often completely forget that they are on. Maybe
45 dB with the fan set to maximum.
Typically, we set the fan speed to "automatic" so the fan speed varies
with the demand on the system. The system slowly ramps up and down to
meet the demand. All fans and the compressor are controlled by VFD's so
nothing cycles on and off. You set the temperature on the remote and the
system heats or cools to maintain that temperature in that room. The
units each have there own remote and you can set the temperature of each
room independently. (You can't set one room to heat and another to cool
if the inside units share an outside unit.)
On the particular model we have, you can chose to set the temperature
sensor on the remote, or on the wall unit, to control the wall unit.
Thus, if you are working at your desk that is some distance from the
wall unit, you set the remote to sense the temperature, and place the
remote near you.
The high SEER demands that the temperature difference between the room
and the finned coil be as low as practical. There is no reason to have
120 F air coming out of the inside unit, unless you have set the desired
room temperature that high. (I think the maximum room temperature set
point is maybe 90 F.) The air coming out of the unit is maybe 5 or 10
degrees different than the desired room temperature.
Folks that have these modern units absolutely love them. We bought one
at first for the master bedroom and the office. After a year, we bought
one for the other side of the house, and then bought one for the garage.
Bill D.
On 11/29/2017 10:13 PM, EVDL Administrator via EV wrote:
On 29 Nov 2017 at 18:14, ROBERT via EV wrote:
A heat pump outputs a register temperature of approximately 90 F. This
low a temperature blowing across your skin is not comfortable to a lot
a people.
I think this is less true of recent heat pumps.
I'd like to hear from someone who owns an EV with a heat pump -- how warm
does the air from the vents feel in the winter?
I think that many or most older heat pumps did have this annoyance. It's
not an EV, but I knew someone who had a late-1990s GSHP (Waterfurnace brand)
at home. The heating air from the vents always felt cool to me, meaning
that it was below body temperature. Ninety deg F would be quite believeable.
That's definitely not the case with my Mitsubishi mini-split from 2013.
Although I haven't measured its outlet temperature in heating mode, most of
the heating seasons it feels quite warm, almost hot. So it has to be well
above body temperature. As the outdoor temperature falls, its outlet
temperature declines too. However, it stays noticeably above body
temperature down to an outdoor temperature of around -15 deg C.
Thus I see no reason that an EV heat pump would have to produce air that
feels cool under most conditions. For the times that it did, I'd expect it
to have auxiliary resistive heat.
David Roden - Akron, Ohio, USA
EVDL Administrator
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