"Christian McArdle" wrote in message
. net...
Soon, you'll get a post from IMM advising you
to get a heat bank instead.
Already posted.
These have certain advantages and disadvantages
compared to an unvented cylinder.
Advantages far outweigh disadvantage. Look...
Advantages of Heat-Banks
- Instant high pressure hot water - When the store has reached temperature
water is delivered instantly at the taps.
- High mains water pressures at up to 10 bar, compared to 3.5 bar with
unvenetd cylinders.
- Very high water flow-rate - The high-end heat-banks have a flow-rate up to
45 litres/min.
- Long efficient boiler burn - Reduces boiler on-off cycling increasing
efficiency, although inefficient boiler cycling is no longer a major problem
with boilers with forced flues.
- Maintains optimum boiler temperature range – using ablending valve the
flow/return of the boiler can be kept to opimum mainatinaing greater
effciencies. The boiler operates at optimum performance.
- Combines the output of the stored water and the boiler – see the DPS GXV
- Cylinder may be smaller for a similar performance - smaler cylinders than
unvented cylinders.
- Cylinder at low pressure - Unlike an unvented cylinder it does not store
water at high pressures.
- Fast cylinder recovery rate - When the boiler is connected directly to the
heat-bank, and not via an indirect coil, the recovery rate is rapid.
Although in some cases a boiler may heat the heat-bank via an indirect coil,
reducing the recovery rate.
- Legionella bacteria eliminated - The Legionella bacteria cannot survive in
the high temperature sealed conditions of a heat-bank.
- No scale build-up in heat-bank – Containing primary and not secondary
fresh water,
there is no scale build-up inside the heat-bank.
- Cold water storage eliminated - No need for cold water storage tanks.
- Solar heating storage - Water heated via solar panels may be stored in the
heat-bank via a solar coil.
- Easy maintenance - If an external plate heat exchanger requires cleaning
or replacing it is a matter of draining down the heat-bank, or closing
isolating vales, and unscrewing the plate heat-exchanger. In some rare
instances plate heat-exchangers are fitted directly inside the heat-bank
preventing on-site maintenance.
- Easy to improve hot water flowrates – By simply adding additional plate
heat-exchangers in parallel, hot water flow rates may be improved. Retrofit
additions are possible if extra bathrooms or showers are installed. This is
impossible with unvented cylinders.
- Stored water vessel need not be cylindrical – As no internal coil is used
for hot water heat transfer the stored water vessel may be any shape, as
opposed to a thermal store which has to be cylindrical for maximum
efficiency. This has advantages where space is limited.
Disadvantages of Heat-Banks
- The store needs be near fully temperature to supply baths - Before any hot
water is drawn off, the store must be up to temperature. Many later
versions use a blending valve on the return to the boiler to ensure only up
to temperature water is pumped into the store by the boiler. This prevents
agitation of the stored water, and aiding heat stratification within the
store giving useful water at the top of the store within a shot time. The
water is heated only in one pass through the boiler.
- May not take full advantage of a condensing boiler - Maintaining the
stored water at 75C to 80C results in a generally high boiler return
temperature. This will not take full advantage of a condensing boiler,
which increases in efficiency with lower return temperatures. With the
superior heat stratification of taller cylinders this problem will be
reduced. Condensing boilers with a high operational flow and return
temperature differential are best suited to thermal stores and heat banks.
Overall efficiency with condensing boilers is still very good.
- Lower water temperatures with fast flow-rates - As with Combi boilers,
fast flow-rates through the plate heat-exchanger results in lower water
temperatures. This is not so pronounced with heat-banks as with
thermal-stores. This also applies to unvented cylinders and combi's. With
a heat bank, extra plate heat-exchangers can be fitted to increase flow
rates.
They require the boiler to heat at a
higher temperature,
See above.
they have lower flow rates.
No so. They can operate up to 10 bar pressure. Unveneed cylinders can only
operate up a typical 3.5 bar.
However, they are simpler to
install and don't require the complicated
safety systems that unvented
cylinders need. (There are plenty more issues
on both sides of that one).
Advantages mainly to heat banks by miles.
---
--
Checked by AVG anti-virus system (
http://www.grisoft.com).
Version: 6.0.507 / Virus Database: 304 - Release Date: 04/08/2003