JackofAll Posted November 27, 2023 Share Posted November 27, 2023 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.. Link to comment Share on other sites More sharing options...
SteamyTea Posted November 28, 2023 Share Posted November 28, 2023 As the unit is oversize, are they saying that mean it is over ventilating the house all the time? If so, ditch them right away. It is the mass flow rate that is important, not the physical size/potential maximum extract rate. Link to comment Share on other sites More sharing options...
JohnMo Posted November 28, 2023 Share Posted November 28, 2023 There should be no issue with an oversized unit, but if they don't understand it has to be adjusted to suit the install, and when set up currently it will not be over ventilating, they are Muppets and walk away. Link to comment Share on other sites More sharing options...
Coanda Posted November 28, 2023 Share Posted November 28, 2023 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. Link to comment Share on other sites More sharing options...
JackofAll Posted November 28, 2023 Author Share Posted November 28, 2023 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? Link to comment Share on other sites More sharing options...
ProDave Posted November 28, 2023 Share Posted November 28, 2023 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. Link to comment Share on other sites More sharing options...
SteamyTea Posted November 28, 2023 Share Posted November 28, 2023 35 minutes ago, JackofAll said: least 200 m3/h How large is the house? Link to comment Share on other sites More sharing options...
JackofAll Posted November 28, 2023 Author Share Posted November 28, 2023 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. Link to comment Share on other sites More sharing options...
JackofAll Posted November 28, 2023 Author Share Posted November 28, 2023 1 hour ago, SteamyTea said: How large is the house? 179sqm Link to comment Share on other sites More sharing options...
SteamyTea Posted November 28, 2023 Share Posted November 28, 2023 22 minutes ago, JackofAll said: 179sqm 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. Link to comment Share on other sites More sharing options...
JackofAll Posted November 28, 2023 Author Share Posted November 28, 2023 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? Link to comment Share on other sites More sharing options...
JohnMo Posted November 28, 2023 Share Posted November 28, 2023 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. Link to comment Share on other sites More sharing options...
SteamyTea Posted November 28, 2023 Share Posted November 28, 2023 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. Link to comment Share on other sites More sharing options...
JackofAll Posted November 28, 2023 Author Share Posted November 28, 2023 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. Link to comment Share on other sites More sharing options...
JackofAll Posted November 28, 2023 Author Share Posted November 28, 2023 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. Link to comment Share on other sites More sharing options...
JohnMo Posted November 28, 2023 Share Posted November 28, 2023 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 Link to comment Share on other sites More sharing options...
Conor Posted November 28, 2023 Share Posted November 28, 2023 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". Link to comment Share on other sites More sharing options...
JackofAll Posted November 28, 2023 Author Share Posted November 28, 2023 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? Link to comment Share on other sites More sharing options...
JackofAll Posted November 28, 2023 Author Share Posted November 28, 2023 What unit do you have Conor? Link to comment Share on other sites More sharing options...
Conor Posted November 28, 2023 Share Posted November 28, 2023 Salda smarty. Do not reccomend. Link to comment Share on other sites More sharing options...
JackofAll Posted November 28, 2023 Author Share Posted November 28, 2023 4 hours ago, Conor said: Salda smarty. Do not reccomend. Thanks, have to say I've never heard of them. Link to comment Share on other sites More sharing options...
SteamyTea Posted November 28, 2023 Share Posted November 28, 2023 Is it BPV that do the free estimates and calculations? Link to comment Share on other sites More sharing options...
Coanda Posted November 28, 2023 Share Posted November 28, 2023 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. Link to comment Share on other sites More sharing options...
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