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Just received a quote and have been told that because the unit(domekt cf700 (H) ) they are suppling is over sized in capacity by 50-60% there is no need for boost  function. "Normal mode effectively removes moisture and steam". One girl takes 40 min showers, would imagine boost would be necessary in this scenario? Thoughts..

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I would ask why they are supplying an over size unit.

Wouldn't that be like putting in a proper size unit and running it on boost all the time.

 

Who would want to do that.

Plus it's likely more spendy than the correct size.

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Hi guys, thanks for replies, please see below taken from correspondence. 

 

To comply with part F of the Regulation, we believe the house should have a continuous supply of at least 200 m3/h. Therefore, we suggest a system with a larger unit that operates at 50-60% capacity to minimize power consumption and noise, even at night. Our design ensures a supplied fresh air rate of up to 300 m3/hour, and the system operates in normal mode at all times without the need for a boost mode. The normal mode effectively removes moisture and steam from bathrooms while maintaining ideal indoor air comfort.

 

Did I misinterpret?

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Building regs still requires a boost mode above the normal continuous rate.

 

Are you sure they have done their sums properly for a continuous running ventilation system?  300m3/h sounds way too high, like they have taken the rates for intermittent extract fans?  I would double check that.

 

And many of us here run our systems at a much lower rate without problem.

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1 hour ago, ProDave said:

Building regs still requires a boost mode above the normal continuous rate.

 

Are you sure they have done their sums properly for a continuous running ventilation system?  300m3/h sounds way too high, like they have taken the rates for intermittent extract fans?  I would double check that.

 

And many of us here run our systems at a much lower rate without problem.

Will check it out Dave, thanks.

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1 hour ago, SteamyTea said:

If we call that 180 m2 and the height is 5 m, then the volume is 900 m3

 

At 200 m3/h, that is 0.22 ACH.

Thanks Steamy,

Does that mean 22%of total volume of 'stale' air is removed per hour? If so would it make more sense to have a boost mode should one/two showers be taken within an hour. Is .22ACH good or bad?

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1 minute ago, JackofAll said:

Thanks Steamy,

Does that mean 22%of total volume of 'stale' air is removed per hour? If so would it make more sense to have a boost mode should one/two showers be taken within an hour. Is .22ACH good or bad?

Are his calculations correct for volume? If so yes, but if 179 X 2.4 then nearer 0.5 ACH. Which is building regs. And with 2 or 3 in house is over ventilating in practice.

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2 minutes ago, JohnMo said:

Are his calculations correct for volume

Ah, maybe not.  I assumed that was foot print, not total floor area.

My mistake.

 

8 minutes ago, JackofAll said:
1 hour ago, SteamyTea said:

At 200 m3/h, that is 0.22 ACH.

Thanks Steamy,

Does that mean 22%of total volume of 'stale' air is removed per hour?

It means that a fifth of the air in the house is replaced every hour, or on @JohnMo better calculations, half the air is changed every hour.

 

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4 minutes ago, JohnMo said:

 

Are his calculations correct for volume? If so yes, but if 179 X 2.4 then nearer 0.5 ACH. Which is building regs. And with 2 or 3 in house is over ventilating in practice.

Most ceilings are 2.8 with one room vaulted approx 10m x 4.6m x 4.3m and a section of hall also approx 4.9m x 2m x 4.3m vaulted. Probably difficult to calculate without exact measurements. Will sit down and tot it up. There will be 5 in the house.

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16 minutes ago, SteamyTea said:

Ah, maybe not.  I assumed that was foot print, not total floor area.

My mistake.

 

It means that a fifth of the air in the house is replaced every hour, or on @JohnMo better calculations, half the air is changed every hour.

 

Thanks Steamy, made the same error. Think it's 160sqm after subtracting wall thickness.

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28 minutes ago, JackofAll said:

Most ceilings are 2.8 with one room vaulted approx 10m x 4.6m x 4.3m and a section of hall also approx 4.9m x 2m x 4.3m vaulted. Probably difficult to calculate without exact measurements. Will sit down and tot it up. There will be 5 in the house.

Certainly if you use passivhaus calculation method, you only work out to 2.5m high irrespective of actual heights. Maybe the same for building regs also 

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We've oversized units, has four fan speed modes. Runs on the second step most of the time, occasionally drops down to the lowest mode temp / humidity dictate. Never known it to jump up a step to deal with excess humidity.

 

Make sure the unit can be set at a lower speed... Ours is about half of the "requirement".

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2 hours ago, JohnMo said:

Certainly if you use passivhaus calculation method, you only work out to 2.5m high irrespective of actual heights. Maybe the same for building regs also 

Thanks John, as with many other building reg minimums it's better to exceed their target, so how is that achieved in relation to MHRV? Is it all the air tightness detailing at the various junctions?

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9 minutes ago, SteamyTea said:

Is it BPV that do the free estimates and calculations?

BPC.

But it's only free if you buy from them, which means they have it built into their pricing structure.

You pay a deposit which is not refundable but offset against a purchase.

Nothing in this life is free. :)

 

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