ASHRAE Journal - January 2015 - 65

COLUMN REFRIGERATION APPLICATIONS
Andy Pearson

Home Is Where the Heat Is
BY ANDY PEARSON, PH.D., C.ENG., MEMBER ASHRAE

There are lots of things that can be used to heat our homes. Open fires or log-burning
stoves give a fantastic sense of homeliness and for me always take me straight back
to holidays in the north of Scotland where a roaring fire was very welcome, even on
a summer evening. Nowadays, it would be called a biomass thermal processor; back
in the day we just knew that if we chopped enough logs through the day the reward
would be to sit in front of a roaring fire watching the flames dance and hearing the
distinctive crackle of burning pine.
Other options, for those who don't like to get their
efficient when you need them most. "Just as the price of
hands dirty, whether before or after combustion, vary
eggs goes up, the hens go off the lay" as my Dad used to
widely from country to country. In the United States
say (quoting from Para Handy, I think).
ducted air systems are very common, with a furnace in
The challenges facing the growth of the domestic heat
the basement providing warm air throughout the home. pump market vary widely from country to country. What
In Europe, particularly Northern Europe, furnaces are
seems sensible, logical and even intuitive in one maralso common, although usually called boilers, and the
ket makes no sense at all in another context. However,
heat is distributed round the house by pumpMake mine a heat pump. systems with apparently contradictory requireing water through small diameter distribution
ments, such as ducted air versus pumped hot
pipes laid below the floor and behind the skirtwater, share some common features. Operating
ing boards. Each room is fitted with a radiator-
the system at as low a temperature as possible
a metal heat exchanger fixed to the wall that
is irrelevant for traditional combustion-based
warms the air and allows it to circulate round
heating but is crucially important for the
the room.
economy of heat pump systems. Achieving this
LORD KELVIN
It is interesting to note that the "boiler" doesn't
change of habit requires modification of the
actually boil the water and the "radiator" works primarbasic design of our homes with greater emphasis on
ily by convection, not radiation, but in both cases the
techniques such as underfloor heating, which have not
names have stuck and are here to stay. In some more
been so important since the days of ancient Rome.
modern houses the heating is partly or wholly through a
When Lord Kelvin was engaged in the development of
grid of pipes laid into the floor. This is cheap to do durthe hydroelectric power plant at Niagara, as President of
ing construction, but it is an expensive retrofit. It also
the International Niagara Commission, he wrote, with
requires the water temperature to be lower than for a
reference to the use of heat pumps, "When Niagara is set
radiator-typically about 95°F (35°C) for underfloor heat- to work for the benefit of North America through electric
ing whereas up to 180°F (82°C) is required for radiators.
conductors, it will no doubt be largely employed for the
In Japan, where space is often even more at a premium
warming of houses over a considerable part of Canada
than in Europe, split air-conditioners with a heat pump
and the United States." Kelvin was infamous in his latter
function are very common. Heating is provided by switch- years for making dogmatic statements that proved to be
ing the function of the indoor and outdoor units so that
wrong, such as "X-rays will prove to be a hoax;" "Radio has
outdoor air is cooled in winter to provide room heating.
no future;" and perhaps most famously "Heavier than air
This is particularly effective when the ambient is merely
flying machines are impossible." However, in the case of
cool but not so good in much colder climates. This is
Niagara and heat pumps the verdict seems to be "not yet."
the Achilles heel of domestic heat pumps: they are least
Andy Pearson, Ph.D., C.Eng., is group engineering director at Star Refrigeration in Glasgow, UK.
JAN UARY 2015

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