[PPT] - in the Passivhaus Alan Clarke, Nick Grant. alan@arclarke.co.uk PowerPoint Presentation

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The importance of hot water system design in the Passivhaus

Alan Clarke, Nick Grant. alan@arclarke.co.uk nick@elementalsolutions.co.uk

The Authors would like to thank the AECB and Passnet for their assistance towards presenting this paper.

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UK hot water system

Kitchen Cylinder Boiler Bathroom

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fuel Cold water boiler p p Primary loss Storage loss Distribution loss Heat gains to room Heat gains from room Building heat loss Solar gains Flue loss Heat gains to room Bath Heating system Water to drain Optional secondary circulation Utilisation factor

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Example of hot water system

Hot water use is 25 litres/person/day
Gas boiler
Cylinder has 50mm insulation
7m from boiler to cylinder
Secondary circulation

– Insulated 12mm – Pumped 24 hours/day

So not best practice, but could be a Passivhaus

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15 30 45 60 heating hot water use cylinder loss primary loss secondary loss Heat demand kWh/(m².a) secondary loss primary loss cylinder loss hot water use secondary loss utilised primary loss utilised cylinder loss utilised space heating

The losses add up

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Hot water losses > fabric losses

(if you’re not careful)

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Behaviour

5379 131 14 15 12 Branwen 239 6 4 4 7 Blodwen 1255 31 7 7 12 Badden kWh/y m3/y Uses/ week Time (min) Flow (l/min) Person

Same 12 litre/minute shower head, Badden maybe average, Blodwen doesn’t like washing! Branwen loves the shower – and uses 20 times more hot water than Blodwen

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Water energy model

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fuel Cold water boiler p p Primary loss Storage loss Distribution loss Heat gains to room Heat gains from room Building heat loss Solar gains Flue loss Heat gains to room Bath Heating system Water to drain Optional secondary circulation Utilisation factor

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“micro-component”

Usage figures for

– Washing machine & dishwasher – WC – Basin – Bath – Shower – Kitchen sink

Usage based on measurements in UK homes

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Energy Saving Trust Study

Specifically measured hot water
Average 122 litres/house/day

– 40 litres/day + 28 litres/person/day

Hot water delivery temperature 52°C
Energy use for water used was 30% higher

than PHPP assumption

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Principles of model

Account all the heat flows
See where the heat ends up
System losses

– Cylinder – Boiler and primary circuit – Pipes from cylinder to taps

Gains from hot water in bathroom
Losses to cold water in bathroom

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Based on scientific measurement

In the bath…

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Bath Cooling curve

15.0 ¡C 20.0 ¡C 25.0 ¡C 30.0 ¡C 35.0 ¡C 40.0 ¡C 45.0 ¡C 50.0 ¡C 55.0 ¡C

: 1 : 2 : 3 : 4 : 5 : 6 : 7 : 8 : 9 : 1 : 1 1 : 1 2 : 1 3 : 1 4 : 1 5 : 1 6 : 1 7 : 1 8 : 1 9 : 2 : 2 1 : 2 2 : 2 3 : 2 4 : 2 5 : 2 6 : 2 7 : 2 8 : 2 9 : 3 : 3 1 : 3 2 : 3 3 : 3 4 : 3 5 : 3 6 : 3 7 : 3 8 : Minutes:seconds ¡C

Room temperature Bath temperature

Got out Pulled plug

Thermal gains

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And the WC cistern heat loss

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WC and room temperatures 10 second sample

5 7 9 11 13 15 17 19 21 23 12:50:00 14:26:10 16:02:20 17:38:30 19:14:40 20:50:50 22:27:00 00:03:10 01:39:20 03:15:30 04:51:40 06:27:50 08:04:00 09:40:10 11:16:20 12:52:30 14:28:40 16:04:50 17:41:00 19:17:10 20:53:20 22:29:30 00:05:40 01:41:50 03:18:00 04:54:10 06:30:20 08:06:30 09:42:40 11:18:50 12:55:00 14:31:10 16:07:20 17:43:30 19:19:40 20:55:50 22:32:00 00:08:10 01:44:20 03:20:30 04:56:40 06:32:50 08:09:00 09:45:10 11:21:20 12:57:30

cistern room

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The model: a big spreadsheet

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Losses fairly independent of water use

15 30 45 60 75 90 low medium high Heat demad Kwh/(m².a) Hot water use secondary loss primary loss cylinder loss hot water use secondary loss utilised primary loss utilised cylinder loss utilised space heating

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Reducing losses

Cylinder insulation
Primary distribution
Secondary distribution

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Solving the problems

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How much insulation?

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Circulation loops

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Draw-off deadlegs

10 20 30 40 50 60 0.5 1 1.5 2 2.5 3 Temperature at tap C Litres delivered

Measured results.

dead leg = 13.5m x 56ml/m = 0.76 litres pipe warming up

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Deadleg: pipe from cylinder to tap

Draw-off lag
Waste of water while waiting for hot
Hot water left in pipe cools down
Depends on volume = length x area

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Use simple microbore manifolds and flexible pipework

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Solutions

Layout – less than 6m cylinder to kitchen sink
Lower flow rates = smaller pipes
Mains pressure hot water = smaller pipes
Use manifold and radial piping, PEX or copper
10mm usually fine for basins, showers, sinks

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Boiler – cylinder length

Kitchen Cylinder Boiler Bathroom

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Improved systems

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Overall plan for UK houses

100mm+ insulation on cylinder
Heat trap connections
Microbore < 6m length
No need to insulate the distribution
Primary pipework < 3m
Primary pipework 25mm insulation

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Summary

Designers limited in effect on hot water usage
Designers can control hot water losses
These losses are important
We can reduce them with good design

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Conclusions

For a domestic Passivhaus, DHW use is > space

heating and losses can equal fabric losses

Losses largely independent of water use but

dependent on design.

Losses can be reduced significantly

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Previous work

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