27. Rod Speed
Dec 16, 3:47 pm show options

Newsgroups: alt.home.repair, sci.engr.heat-vent-ac,
misc.consumers.frugal-living
From: "Rod Speed" - Find messages by this author

Date: Sat, 17 Dec 2005 07:47:00 +1100
Subject: prog. therm. and heat pump questions
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Abby Normal wrote



When it is sized to the load the problem is it would only shut off for
an hour or two as the house cooled, then it would run steady until
after the sun came up to catch up. No real point in setting back.


That is just plain wrong. The whole point of a set back is that
less is pumped at the setback temp because the losses are lower.
How much lower depends on how well insulated the house is.

The whole point of set back is to lower the temperature for a
while.This would imply that the house cools down and the systems stops
running during this cool down period. Then it would run less per hour
due to the setback indoor temperature until such a time that it need to
start warming up the house so that it was back up to temperature
perhaps when the occupants awoke or perhaps returned home from work.

The problem is shortly after the temperature dropped to the setback
temperature, the heat pump would end up running steady just to get back
up to temperature.

Typically in the temperate states where air source heat pumps are used,
they are sized with the cooling load in mind and use the heat strips.
One sized for the full heat load will be grossly oversized for cooling
resulting in summer time humidity control problems.

The only way set back works with a heat pump is if it is grossly oversized.


Wrong again.

No not wrong just unsucessful in educating you.


All that accomplishes is set back without auxiliary heat.
It would short cycle inefficiently except for when it was
trying to recover from a set back.


Not if you one of the systems sized so that doesnt happen.

So you are saying size one for the cooling load, one for the heating
load and one for speedy recovery from set back then?

Three heat pumps now. Plus all the ductwork and backdraft dampers.
Let's try to keep this practical and not go to hypothetical extremes to
prove this is possible. Noah er I mean Nick is a bad influence on you.

In an environment with an ambient dewpoint above 60F there will
be problems with a grossly oversized system in cooling mode.


Again, not if you have more than one system.

Well like I said if you want to install three heat pumps, knock
yourself out.