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Ground
Source Heat Pumps - Cylinder & Hot Water Efficiency |
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If
you like the idea of doing your bit for the environment,
whilst enjoying the benefits, then pick up the
phone or fill out the form on the contact page.
All our details
along with a web form can be found
on the contact page click
here
Tel:
0114 287 0723 |
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Which
Cylinder For My Heat Pump?
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There
are many different cylinder manufactures
and they each have their own standard
product range. On top of this; most
manufacturers will ‘tailor
make’ you a cylinder to your
to your exact specification and requirements,
and they have it down to a fine art.
In some cases a cylinder can be ordered
in the morning and collected in the
afternoon!
There are plenty of variables when choosing a cylinder and
it is not one size fits all; the key is to select the right
cylinder for your job. People refer to them as a battery because
they are a store of ‘charged’ hot water. It is
important to find the balance between storage capacity, demand,
and heat input energy required for your battery. These questions
all relate to size and occupancy level of your property including
the amount of outlets within kitchens, bathrooms and en-suites,
and in particular; mixer showers. Further tips
and measures about containing hot water flow rate are available
further down the page.
We then have to consider the heat source for our cylinder or
battery, which in our case is an air source heat pump. We recommend
using a thermal store although unvented
cylinders can also be used. Thermal stores are popular
on the continent and particularly in Germany where hot water
regulations are more stringent than ours. Their popularity
is due directly to their efficient nature, versatility of connecting
to multiple energy sources and quality of mains pressure supply.
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Within
air source heat pump systems a buffer
vessel or buffer tank is required,
a thermal store will eliminate the
need for a buffer tank and provide
a host of other benefits.
Explained firstly;
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Used
in conjunction with air source heat
pumps, a buffer
tank is installed in addition to the
hot water cylinder, within the primary
heating circuit. It increases the volume
of water a heat pump has to heat, allowing
excess heat to be stored within the
buffer tank until it is required. Buffer
tanks increase response times when
the heating is turned on due to this
store of heat. Buffer vessels reduce
the short cycling of the heat pump,
and increase COP and lifespan of the
heat pump. The diagram below shows
a buffer tank in conjunction with a
domestic hot water unvented cylinder.
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| Air
Source Heat Pump with Unvented Cylinder |
The
diagram above shows a heat pump coupled
with an unvented cylinder. Unvented
cylinders are full of potable sanitary
water, safe for us to drink and supplied
at mains pressure. This is a key benefit
of an unvented system and means we
can, within reason supply multiple
hot water outlets (like showers) at
the same time. A combination boiler
or gravity based system would not produce
enough pressure to do this.
The primary water in the flow from the air source heat pump
is used to heat up the water in the cylinder through an indirect
method; it is pumped through the coil at the bottom of the
unvented cylinder. In the diagram above, the unvented cylinder
is labelled as ‘the tank’ while the coil is labelled
as the ‘heat exchanger’ which is exactly what it
is.
As heat pumps run at lower temperatures, it is imperative that
the coil within the cylinder is sized correctly in terms of
exposed surface area in order to achieve the correct transfer
of heat. Failing this the sanitary water within the cylinder
will not get hot enough. All the cylinders we fit come with
a built in immersion heater in order to boost temperatures
when required and also for the legionella protection cycle.
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The
unvented cylinder in the diagram above
has only a single coil. Twin coil cylinders
are available should you wish to combine
your heat pump with solar thermal panels.
Doing this will increase your systems
efficiency, heat pump COP and electricity
consumption. Solar thermal panels can
produce 80% of your hot water annually,
and even in winter months they can
act as a pre heat for your heat pump.
Again the second solar coil will need
to be sized correctly to your systems
needs, taking into consideration amount
of solar panels and cylinder size.
The size of cylinder you require is linked to your property
size and occupancy level. The recommended amount of daily hot
water per person per day is 45L. Generally, bigger houses will
require bigger cylinders and consideration should be taken
in respect to cylinder location; whether or not it will fit
in the cupboard, through the door way and whether the floor
is strong enough to take the weight when full. Early planning
to a whole system approach is recommended. This will help prevent
problems that could arise at a later stage.
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| "We
ensure all the cylinders we install
are insulated to a high degree and
have low standing losses" |
Air
Source Heat Pump With A Thermal
Store
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A
thermal store is similar in comparison
to an unvented cylinder, not least
in appearance.
They are both coated in a super insulated spray foam casing
and they both contain a body of water.
However, they are in fact opposites; the main difference is
within the water they contain and how they function.
An unvented cylinder contains a large amount of sanitary water
which is heated when primary water from the heat pump is fed
through a heat exchanger coil
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A
thermal heat store is a large amount
of primary water kept warm by the heat
pump.
The heat pump feeds water directly into the cylinder. Sanitary
water is fed through a large coil inside, from which it draws
the heat out of the primary water.
Water enters the cylinder cold and exits as hot.
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Sometimes,
instead of a large coil through the
centre of the cylinder a plate heat
exchanger is located on the outside
of the cylinder and hot primary water
from inside the cylinder is used to
heat the cold mains water.
Some manufacturers say this is better for stratification within
the cylinder.
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Underneath all the insulation, thermal store cylinders are generally
constructed of copper unlike the stronger stainless steel casing
required for the pressurised unvented cylinder. The reason for
this difference is that a thermal store (unlike a an unvented
cylinder) is not a pressurised store, it is in fact a ‘vented
system’ all be it a ‘sealed vented system’ meaning
it is not pressurised but also meaning neither the hot water
circuit or the heating circuits are open to the atmosphere because
they are sealed. There is no chance of any air entering the pipe
work to cause problems; so there is no danger of damage or irritation
to any of the system that is usually associated with the ‘old
type’ vented systems.
There are a lot of benefits to a thermal store that make them appealing
in certain situations:
A thermal store allows us to ‘dump heat’ and save it
for later when we need it.
Contribute to both the supply of heat hot water and the supply of
heat to the heating system without the need for a buffer vessel,
unlike an unvented cylinder.
With a thermal store we can connect to multiple sources of heat,
where as with an unvented cylinder you can only have two coils (up
to cylinders of a very large size) before the heat exchange would
not be effective. This means that with only two coils we are limited
to only two inputs of heat, for example the heat pump, and solar
thermal panels.
Due to the pressures within the unvented system it is dangerous and
against regulation to connect an unvented cylinder to a biomass boiler
or wood burning stove etc. However, with the thermal store this is
not a problem due to it being vented low pressure.
The thermal store will however deliver domestic hot water at mains
pressure because the hot water coil or exchanger is connected directly
to the mains.
They offer huge versatility and many options of energy input; we
can connect oil, gas, and bio gas boilers, wood chip, wood pellet
or wood burning stoves, agars, solar thermal panels, air source heat
pumps and ground source heat pumps. Basically anything that can generate
heat, you can plumb in!
There is no danger of lime scale build up within the cylinder in
hard water areas as the water within the cylinder is not been constantly
replaced (like with an unvented cylinder.)
There is no danger of legionella as we are not storing any hot water
we are to draw off.
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| Schematic
Layout Of Thermal Store With Heat Exchanger
On Outside |
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| Hot
Water Savings |
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When
deciding on a thermal store, or any system,
try and think of it as a whole house approach
and address all the issues, making sure you
have all the ‘pieces of the jigsaw puzzle
in place.’
Especially important with a thermal store is mains pressure and flow
rates at the end point of use. This needs to be controlled to achieve
the right balance: Too high a flow rate and not enough energy will
be taken from the exchange within the cylinder to warm the water adequately.
We control this by; fitting pressure reducing valves before the thermal
store, so as not to exceed the limit recommended by the manufacturer.
We also need to watch our water consumption at the end point of use.
Using more hot water than is actually needed not only wastes the water
we pay for but also the energy we use from the thermal store to heat
it (which we also pay for).
Now you may be thinking ‘I agree but when I turn the tap on I
want hot water and I want enough of it! In this situation you can ‘have
your cake and eat it’
At each hot water outlet, shower head or tap we are able to regulate
this consumption without compromising on performance, we fit flow regulators
and aerators: The flow regulator slows the flow of hot water.
The benefit of this is that in turn the pressure is increased; brilliant
for showers.
The aerator then mixes this high pressure jet of water with air to
create a nice creamy flow with a fuller coverage.
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whilst less water is actually supplied it feels
like more, due to the increased pressure and
mix with air. This mix with air also has the
added benefit of preventing splashing. |
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Flow
regulators and aerators will limit flow and
prolong heat reserves, especially in peak demands.
They are the final piece of the puzzle to your
complete energy efficient hot water system
using a thermal store or unvented cylinder.
They are essential when buying new and can
be retrofitted to existing taps.
When you purchase your shower, you should be aware of the following:
 A
fully operational power shower
should use no more than a maximum
of 11 litres per minute
An
Eco Shower uses 7 litres per minute
A
Norwegian Eco Shower uses 4.5 litres
per minute
If you have a 500 litre tank (of which 320 litres is hot water), you
can have:
3
(fully pressurised) showers of
ten minutes' duration, or
5
Eco showers of nine minutes' duration,
or
7
Norwegian Eco Showers of ten minutes'
duration
Building
and insulation standards have improved
considerably over the past number of
years which has meant that it's possible
to reduce boiler and heat pump sizes.
However, simultaneously, our demand for
hot water has increased (more bathrooms,
shower rooms, ensuites, wet rooms, swimming
pools) and this has resulted in driving
the size of boiler and heat pumps back
up again. It is vital that you consider
your hot water requirements and that
your domestic water system is designed
properly. You need to install the appropriate
size tank and pipe to ensure efficiently
delivering enough hot water.
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EFFICIENT
ENERGY SOLUTIONS YORKSHIRE
© 2013
Efficient Energy Solutions Yorkshire. All Rights
Reserved E & O E
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