Difference between revisions of "Increase Hot Water Capacity"

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Does the hot water run out too soon?  
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Does the hot water run out too soon? Some ways to increase capacity:
  
  
==7 ways to increase hot water capacity==
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===Bigger Hot Water Cylinder===
 
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The obvious option is a bigger cylinder. However this isn't always a good option, eg when renting, or if budget is lacking. There are other options.
===Bigger Tank===
 
The obvious option is a bigger tank. Thankfully there are easier ways too.
 
  
  
 
===Higher Thermostat Temperature===
 
===Higher Thermostat Temperature===
The simplest way to increase capacity is to turn the HW thermostat up. This means the hot water is used more slowly, as less of it is needed to bring the shower or bath upto the required temp. Thus your HW lasts longer.
+
The simplest way to increase capacity is to turn the HW [[thermostat]] up. This means the [[Domestic Hot Water|hot water]] is used more slowly, as less of it is needed to bring the shower or bath upto the required temp. Thus the HW lasts longer.
  
 +
If incoming water is 10C, and HW temps are 55C and 75C before and after adjustment, the capacity increase is (75-10)/(55-10) = 1.44 or 44% more.
  
===[[Drain Heat Exchanger]]===
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Avoid temperatures that are a burn risk.
A lot of heat goes down shower drains. Nearly the entire contents of the hot water tank in fact.
 
  
A [[Drain Heat Exchanger]] recovers a good percentage of this heat, returning it to the shower cold feed. So less hot water is needed to bring it upto temp, and the tankful lasts longer.
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A lot of [[Immersion Heaters|electric immersion heaters]] can be set to any desired temperature, even burn risk temperatures such as 95°C. Newer immersion heater [[thermostat]]s can't be set to these elevated temperatures.
  
By [[:Category:Energy Efficiency|reducing energy use]] [[Drain Heat Exchanger|these exchangers]] can pay back their cost in under a year in some cases. For information see the main [[Drain Heat Exchanger]] article.
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Gas [[boiler]] water heating works a bit differently, and the cylinder stat should be set to a temp below the primary circuit temp. If its set higher, the circulation [[Pumps|pump]] will run continuously, using power for no gain. Primary temp varies according to system design and setting, but if the [[Pumps|pump]] runs all day, the cylinder stat is set too high.
  
 +
The possible downsides are the scald risk if too hot, increased [[Limescale|scaling]] in hard [[water]] areas, and increased standing heat loss from the cylinder.
  
===Move Thermostat Lower===
 
HW tank thermostats are typically 2/3 the way down the tank, but are sometimes higher up. HW tanks [[:Category:Heating|heat]] up from the top downwards, and [[Water|water]] below the stat will be at lower temp than the stat setting. Often this cooler water is no more than lukewarm, and this could be heated to gain more HW capacity.
 
  
Moving the thermostat further down will increase the quantity of hot water in the tank. The implications depend on where the stat is in relation to the heating element or built in exchanger.
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===Aeration===
* If the stat was high up and is moved to 2/3 down, things will behave normally after moving
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Aeration of shower and taps reduces water use, making a given amount of hot water last longer. Aerators are cheap and easy to fit to showers.
* If the stat is moved much lower than the exchanger or element, [[:Category:Heating|heating]] that extra bottom zone of the HW tank will take longer, and the top water will get hotter than the stat setting.
 
  
  
===[[Solar Thermal|Solar Preheater]]===
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===Slower booster pump===
A [[Solar Thermal|solar preheater]] produces a batch of warm water which is fed into the tank when hot water is used, rather than the HW tank drawing cold water in as happens with most HW tanks. The result is less energy use and to some extent increased HW output. The amount of output increase will depend on the temperature of the preheat water.
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A [[Pumps|Shower boost pumps]] with no [[Fan Speed Controller|speed adjustment]] can have max flowrate & pressure reduced with a valve, if one isn't already fitted, giving longer shower time.
  
There are several designs of [[Solar Thermal|solar preheater]], with performance varying significantly from one design to another.
+
===Drain Heat Exchanger===
 +
A lot of heat goes down shower drains. Nearly the entire contents of the hot water cylinder in fact.
  
With any [[Solar Thermal|solar thermal]] equipment, it is strongly recommended to assess any proposed system properly before construction, since many designs are unable to pay back their cost. Professionally supplied systems are worse than [[Special:Allpages|DIY]] ones in this respect.
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A [[Drain Heat Exchanger]] recovers a percentage of this [[heat]], returning it to the shower cold feed. So less [[Domestic Hot Water|hot water]] is needed to bring it upto temp, and the [[Domestic Hot Water|hot water]] lasts longer.
  
[[Solar Thermal]]
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By [[:Category:Energy Efficiency|reducing energy use]],  [[Drain Heat Exchanger|these exchangers]] can pay back their cost several times over in some cases. Actual payback depends on system design and use, and only sometimes justifies their use.
  
  
===Use CH Circuit Heat===
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===Move Thermostat Lower===
The [[Central Heating]] radiator circuit contains hot water in winter and prewarmed [[Water]] in summer. It is possible to harvest all this heat and add it to the HW, thereby giving greater HW capacity.
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HW cylinder thermostats are typically 2/3 the way down the cylinder on [[gas]] heated systems, but are sometimes higher up. If higher up, moving it down can increase HW capacity.
  
Ways to arrange this:
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HW cylinders [[:Category:Heating|heat]] up from the top section downwards, and [[water]] below the stat will be at lower temp than the stat setting. Often this cooler water is no more than lukewarm.
* With a [[Thermal Stores and Heat Banks|heat bank]] or [[Thermal Store]], The cold water supply goes through a heat exchanger on the CH circuit before going to the HW heat exchanger.
 
* With a [[Boilers|combi]], the cold water supply to the [[Boilers|combi]] goes through the CH exchanger, thus boosting the [[:Category:Heating|heat]] output for a while.
 
* With a conventional HW tank, the cold feed to the HW tank goes through the CH exchanger.
 
  
====Performance====
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Moving the thermostat down increases HW quantity in the cylinder. The implications depend on where the stat is in relation to the heating element or built in exchanger.
The [[Heat bank]] option uses all the CH heat. It is the most effective option.
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* If the stat was high up and is moved to 2/3 down, things will behave normally after moving
 +
* If the stat is moved lower than the [[Immersion Heaters|electric heating element]], the [[water]] may overheat. This needs to be checked for when the stat is moved, and if it occurs the stat needs to be moved back up. Electrically heated hot water must not be left in an overheating condition.
 +
* If the stat is moved lower than the exchanger in a [[gas]] powered system, the [[water]] doesn't overheat, but the circulation [[Pumps|pump]] runs continuously. If this occurs, move the stat further up to avoid any [[Save Energy & Money|energy waste]].
  
How much boost the [[Boilers|combi]] option gives depends on system design and [[Boilers|boiler]] characteristics. It may prove to be advantageous to restrict the CH heat exchanger size to ensure the [[Boilers|boiler]] does not modulate at first during HW heating.
 
  
The conventional tank variant can only benefit from part of the CH circuit's [[:Category:Heating|heat]] capacity. Once the CH circuit drops below usable HW temp, the remaining [[:Category:Heating|heat]] will not be used in a way that increases HW output at the tap. Hence there will be no HW boost in summer. Although capacity is not improved as much, HW recovery times will be improved all year round.
+
===Solar Preheater===
 +
A [[Solar Thermal|solar preheater]] produces a batch of warm water which is fed into the cylinder when [[Domestic Hot Water|hot water]] is used, rather than the HW cylinder drawing cold [[water]]. Whether this increases effective HW capacity depends on the temp of the incoming solar preheated water, and what the HW is used for.
 +
* Hot preheated water increases effective capacity
 +
* Warm preheated water increases effective capacity with baths, but not other uses
  
 +
There are several designs of [[Solar Thermal|solar preheater]], with performance, cost, payback and ease of fitting varying widely.
  
===Electric Boost===
+
With any [[Solar Thermal|solar thermal]] equipment, any proposed system needs proper assessment before construction, as many designs never pay back their cost. Professionally supplied systems are worse than properly designed [[Special:Allpages|DIY]] ones in this respect.
This one is just an idea for discussion, and has not been tried by the author. You should not try it without finding out whether it would work ok first.
 
  
Add a 3kW [[:Category:Heating|heater]] to the cold water feed at the shower & bath taps, along with a low temperature thermostat to avoid uncomfortable temperature rise.
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See [[Solar Thermal]]
 
 
If [[:Category:Heating|heater]] flow is restricted, it may be possible to split the feed into 2 parallel pipes, one that goes through the [[:Category:Heating|heater]] and one that contains an isolating valve. The 2 feeds are then reunited. Adjustment of the iso valve determines the flow sharing.
 
 
 
By prewarming the cold feed, less HW is needed, so the tanked HW lasts longer.
 
 
 
Another variant is to add a 3kW heater to the [[Boilers|combi]] heated water output (or possibly cold water input), and trigger it by a flow switch on the shower & bath hot water feed.
 
  
  
 
==See Also==
 
==See Also==
[[Special:Allpages|Wiki Contents]]
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*[http://groups.google.co.uk/group/uk.d-i-y/browse_frm/thread/3ea5694c00d8ff07 discussion of these ideas] on the uk.d-i-y newsgroup
 
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*[[Special:Allpages|Wiki Contents]]
[[Special:Categories|Wiki Subject Categories]]
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*[[Special:Categories|Wiki Subject Categories]]
  
  
Line 76: Line 68:
 
[[Category:Plumbing]]
 
[[Category:Plumbing]]
 
[[Category:Fault Finding]]
 
[[Category:Fault Finding]]
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[[Category:Bathrooms]]
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[[Category:Domestic Hot Water]]
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[[Category:Energy Efficiency]]

Latest revision as of 18:50, 7 June 2012

Does the hot water run out too soon? Some ways to increase capacity:


Bigger Hot Water Cylinder

The obvious option is a bigger cylinder. However this isn't always a good option, eg when renting, or if budget is lacking. There are other options.


Higher Thermostat Temperature

The simplest way to increase capacity is to turn the HW thermostat up. This means the hot water is used more slowly, as less of it is needed to bring the shower or bath upto the required temp. Thus the HW lasts longer.

If incoming water is 10C, and HW temps are 55C and 75C before and after adjustment, the capacity increase is (75-10)/(55-10) = 1.44 or 44% more.

Avoid temperatures that are a burn risk.

A lot of electric immersion heaters can be set to any desired temperature, even burn risk temperatures such as 95°C. Newer immersion heater thermostats can't be set to these elevated temperatures.

Gas boiler water heating works a bit differently, and the cylinder stat should be set to a temp below the primary circuit temp. If its set higher, the circulation pump will run continuously, using power for no gain. Primary temp varies according to system design and setting, but if the pump runs all day, the cylinder stat is set too high.

The possible downsides are the scald risk if too hot, increased scaling in hard water areas, and increased standing heat loss from the cylinder.


Aeration

Aeration of shower and taps reduces water use, making a given amount of hot water last longer. Aerators are cheap and easy to fit to showers.


Slower booster pump

A Shower boost pumps with no speed adjustment can have max flowrate & pressure reduced with a valve, if one isn't already fitted, giving longer shower time.

Drain Heat Exchanger

A lot of heat goes down shower drains. Nearly the entire contents of the hot water cylinder in fact.

A Drain Heat Exchanger recovers a percentage of this heat, returning it to the shower cold feed. So less hot water is needed to bring it upto temp, and the hot water lasts longer.

By reducing energy use, these exchangers can pay back their cost several times over in some cases. Actual payback depends on system design and use, and only sometimes justifies their use.


Move Thermostat Lower

HW cylinder thermostats are typically 2/3 the way down the cylinder on gas heated systems, but are sometimes higher up. If higher up, moving it down can increase HW capacity.

HW cylinders heat up from the top section downwards, and water below the stat will be at lower temp than the stat setting. Often this cooler water is no more than lukewarm.

Moving the thermostat down increases HW quantity in the cylinder. The implications depend on where the stat is in relation to the heating element or built in exchanger.

  • If the stat was high up and is moved to 2/3 down, things will behave normally after moving
  • If the stat is moved lower than the electric heating element, the water may overheat. This needs to be checked for when the stat is moved, and if it occurs the stat needs to be moved back up. Electrically heated hot water must not be left in an overheating condition.
  • If the stat is moved lower than the exchanger in a gas powered system, the water doesn't overheat, but the circulation pump runs continuously. If this occurs, move the stat further up to avoid any energy waste.


Solar Preheater

A solar preheater produces a batch of warm water which is fed into the cylinder when hot water is used, rather than the HW cylinder drawing cold water. Whether this increases effective HW capacity depends on the temp of the incoming solar preheated water, and what the HW is used for.

  • Hot preheated water increases effective capacity
  • Warm preheated water increases effective capacity with baths, but not other uses

There are several designs of solar preheater, with performance, cost, payback and ease of fitting varying widely.

With any solar thermal equipment, any proposed system needs proper assessment before construction, as many designs never pay back their cost. Professionally supplied systems are worse than properly designed DIY ones in this respect.

See Solar Thermal


See Also