Overly complicated UFH?

[ChrisInKent]

I’m after some advice please on UFH.

 

After reading this forum we asked the UFH company we’ve been working with to revise their design (which we have paid £100s for). We asked for a simple 20 degree zone for living downstairs. Their design had each room with a different temp from 18-21. We also wanted an 18 degree zone for upstairs (bedrooms). We’re not bothered with warm bathroom floors which their design had at 23 degrees. 

So the ask was for 2 zones instead of 10-12. 
 

They have come back with a no, they’re happy to install as designed and then we can change it later if we want. Their rationale is that the design follows certain principles which allow them to provide the ongoing warranty and support, a 2 zone system wouldn’t be possible to do this. 
 

Does that make sense? When others on this forum talk about 2 zones do you in fact have multiple zones running at one temp and multiple others running at a different temp? 
 

is a 2 zone system possible? 

 

Edited October 9 by ChrisInKent

[JohnMo]

Sorry but are they fit for purpose as a designer.

 

With LoopCad (UFH design tool) you can easily match heat demand to the amount of pipe in the room. Or you can install more pipe and balance the flow rates to get correct room temps.

 

It would appear their design is basically bounce room temps on a thermostat to manage room temperature.

 

How are you heating the water, boiler or heat pump?

 

 

[ChrisInKent]

Yes their design is a thermostat for every single room. 
 

we are using an ASHP for heating and DHW. Same company refuse to use less than 1.0 air change in their calculations as we haven’t proven it yet (house isn’t built yet so they are using 2.5 to calculate) and won’t factor in the MHVR either so that’s been causing alarm bells. We are planning close to passive. I calculated heat loss 4.5 and they are quoting for a 10 or 12W pump. They said they might include MHVR at 50% heat recovery (we’re expecting 80%). Wondering if we should cut our losses and start again…

[Chanmenie]

What was your heat loss calc in watts, if you are near passive house standards 10 - 12 KW sounds way too much unless you’re 400m2 ? 
 

My experience is most of the UFH designers don’t understand ASHP’s 

 

what’s your floor make up and how much insulation under the UFH pipes ?

[ChrisInKent]

Sorry @Chanmenie I should have written it as 4.5 watts. We are going to be 200m2, super insulated, taped to less than 1.0 air changes but aiming even lower, triple glazed, MHVR system which aims for 85% heat recovery, 160mm insulation on top of the beam and block/membrane under the UFH and then a 100mm polished concrete floor over the UFH. 

[JohnMo]

Keep it simple

Get local plumber to install UFH on ground floor only (plus any upstairs bathrooms). Set ground floor UFH on 150 to 200mm centres throughout. Any bathrooms on 100mm centres due to less usable areas. Buy a Panasonic heat pump to suit your heat loss, a heat pump cylinder (any make) with at least 3m2 coil.  Manifold for UFH, no pump, no mixer, a 28mm diverter valve. Self install or direct plumber and electrician.

 

Use Panasonic controller as a single over temp thermostat, run system on a very small weather comp curve. Possibly starting at 15 Outside and 25 deg flow and -5 outside and 28-32 deg flow. Run everything as single zone.  Provision with option to install electric panel heaters in bedrooms, but don't install unless you need them once moved in. Add electric towel rads to bathrooms use around 500W plus ones and get an external timer thermostat for them.

[Chanmenie]

14 minutes ago, ChrisInKent said:

Sorry @Chanmenie I should have written it as 4.5 watts. We are going to be 200m2, super insulated, taped to less than 1.0 air changes but aiming even lower, triple glazed, MHVR system which aims for 85% heat recovery, 160mm insulation on top of the beam and block/membrane under the UFH and then a 100mm polished concrete floor over the UFH. 

I think you mean 4.5 KW ( which seems high given you said near passive house spec ) in which case you really don’t need 10-12 kw ASHP 

my build is 190m2 my heat loss calc at -5 is 3kw so I have a 4KW ASHP.

I had previously been told you have to make the heat pump bigger to allow for DHW but that’s not true as I don’t believe the pump will heat both at the same time 

[JohnMo]

1 minute ago, Chanmenie said:

had previously been told you have to make the heat pump bigger to allow for DHW but that’s not true as I don’t believe the pump will heat both at the same time 

Not quite correct.

 

If you heat demand was 4kW and you install a 4kW output heat pump at your lowest design temp. The coldest day would require 4 x 24 or 96kWh for the 24 hrs. Now if you take 2 hrs to heat DHW you now only have 22 hrs to deliver 96kWh, so you have a short fall in available energy.

[Chanmenie]

1 hour ago, JohnMo said:

Not quite correct.

 

If you heat demand was 4kW and you install a 4kW output heat pump at your lowest design temp. The coldest day would require 4 x 24 or 96kWh for the 24 hrs. Now if you take 2 hrs to heat DHW you now only have 22 hrs to deliver 96kWh, so you have a short fall in available energy.

Yeah I get that @JohnMo but in lots of cases a heat pump is recommended way over the the heat loss.

my heat pump will heat my 190L in considerably less that 2hrs.

And in your example would the pump actually be running for 24hours ? That would be a bit expensive, how long does yours run for ?

[SteamyTea]

5 hours ago, ChrisInKent said:

which we have paid £100s for

Can you get that back?

 

 

[ChrisInKent]

30 minutes ago, SteamyTea said:

Can you get that back?

 

 

Non refundable  

[SteamyTea]

32 minutes ago, ChrisInKent said:

Non refundable

Maybe Section 75 or a small claims court action if you believe that the report was not fit for purpose i.e. not what you asked them to do.

[joth]

3 hours ago, JohnMo said:

Use Panasonic controller as a single over temp thermostat, run system on a very small weather comp curve

This isn't compliant with part L though is it. That requires at least 2 zones (and recommends one per room, which will be where the OP's installer is getting that from)

 

[ChrisInKent]

1 hour ago, joth said:

This isn't compliant with part L though is it. That requires at least 2 zones (and recommends one per room, which will be where the OP's installer is getting that from)

 

 

I had a look at the Part L info but can’t see this prevents 2 zones being used. The clause (5.20) says one thermostatic control per room but goes on to say heating may be controlled for each heating zone rather than individual rooms ‘where justified’.
 

In 5.21 it says justification includes where ‘2 adjacent rooms have a similar function and heat requirement’ which I read as allowing me to treat the ground floor living areas (kitchen dining living utility) as one zone as we want them all at 20 degrees. 

[Mike]

56 minutes ago, ChrisInKent said:

I had a look at the Part L info but can’t see this prevents 2 zones being used.

You can indeed use only 2 zones and meet Plat L. If you have a well insulated home that's likely to be recommended by everyone here, as above.

 

However official 'best practice' is still for one thermostat per room so, in the absence of any instructions from you to the contrary, your designers have a valid reason for having designed it as they have. As they seem to be supplying and installing it, I imagine they have a financial incentive too.

 

Your options now include:

• persuading them to simplify the design according to your new request
• installing their existing design anyway (after getting their confirmation that it can achieve the temperatures you want - probably not an issue)
• cutting your losses and going elsewhere / designing it yourself - for example using LoopCad

[TerryE]

6 hours ago, ChrisInKent said:

Sorry @Chanmenie I should have written it as 4.5 watts. We are going to be 200m2, super insulated, taped to less than 1.0 air changes but aiming even lower, triple glazed, MHVR system which aims for 85% heat recovery, 160mm insulation on top of the beam and block/membrane under the UFH and then a 100mm polished concrete floor over the UFH. 

 

We've lived in a 3 storey new build with a comparable spec for 7 years now.  Our ACH is around 0.5. We have an MBC WarmSlab that's 100 mm reinforced concrete on ring-beams encased in (mostly) 300 mm structural EPS and UFH embedded in the concrete raft, so ground floor only.  The UFH is run as a single zone and heated by a single 3kW inline resistive heater.  We keep the whole ground floor 24 × 7 within a ~ 1°C tramline of 22½°C, the 1st floor is typical 1-2°C cooler in peak midwinder, though I do use an 1kW oil-filled rad (controlled by my CH system) on the 1st floor for the peak midwinter period.  My son's bedsit in the warm loft is mostly heated by his Games PC and huge TV screens. 🤣

 

The house was built as ASHP ready, but we put the inline heater as a stopgap until we had confirmed the heating characteristics and loses of the house.  However in practice, the heating costs are relatively small,  and we have never made a payback case to install, maintain and depreciate an ASHP.   We have never missed upper floor CH.  I also use the Green Octopus Agile Tariff so my CH system schedules the CH and HW on-times to buy and use the cheapest half-hourly price slots.

 

I am not necessarily suggesting you do the same, but what I am saying is that for this class of house running the whole GFL as a single zone is entirely workable, and  we use less than 30 kWh heat daily even in cold Dec-Feb, so a ~ 5kW ASHP should be fine for this class of house. With a ~ 10m³ slab acting as a thermal store, it is even questionable whether you need a separate buffer tank for the UFH.   I suspect that most ASHP installers have no idea how to design and right-size an ASHP for a (near) passive-class house.

 

[JohnMo]

12 hours ago, joth said:

This isn't compliant with part L though is it. That requires at least 2 zones (and recommends one per room, which will be where the OP's installer is getting that from)

 

Not fully correct 

15 hours ago, JohnMo said:

Add electric towel rads to bathrooms use around 500W plus ones and get an external timer thermostat for them.

Each bathroom is a zone. It has independent zones.

 

Plus if running a heat pump, you comply with the section, where possible weather compensation is to be used.

[JohnMo]

2 minutes ago, Chanmenie said:

but in lots of cases a heat pump is recommended way over the the heat loss

In that case its already taken care off.

 

3 minutes ago, Chanmenie said:

my heat pump will heat my 190L in considerably less that 2hrs.

So will mine, but I heat it twice per day. So might others

 

5 minutes ago, Chanmenie said:

would the pump actually be running for 24hours ? That would be a bit expensive, how long does yours run for ?

If it was rated at max capacity to match heat loss, it should be running full time.

[ChrisInKent]

A bit of an update.

We couldn’t get the original company to change their design or explain their rationale. We went locally to an MCS accredited recommended plumber. They have designed a 2-Zone UFH solution  which we are happy with. Our house has a couple of living areas upstairs (not just bedrooms) so we’re having UFH on both floors. The redone heat calcs show we’ll need a 7kW ASHP no buffer required rather than the 10 or 12kW ASHP with buffer the original company was pushing. 
 

We are feeling more confident that the system is suited the house and we’ve got a local plumber, who is working with us not against us. 

[G and J]

2 hours ago, ChrisInKent said:

A bit of an update.

We couldn’t get the original company to change their design or explain their rationale. We went locally to an MCS accredited recommended plumber. They have designed a 2-Zone UFH solution  which we are happy with. Our house has a couple of living areas upstairs (not just bedrooms) so we’re having UFH on both floors. The redone heat calcs show we’ll need a 7kW ASHP no buffer required rather than the 10 or 12kW ASHP with buffer the original company was pushing. 
 

We are feeling more confident that the system is suited the house and we’ve got a local plumber, who is working with us not against us. 

I’m thinking that either your numbers are wrong or mine are.  Using Jeremy’s spreadsheet our not anywhere near PH 150m2 design looks to need just over 2kW to maintain 20C when it’s -3.5C outside.  
 

I am assuming 87% MVHR efficiency and 0.5AC/h.  The air tightness and form factor (2.75) are the only PH ready things in the place really. 
 

I get the idea that an oversized heat pump lasts longer and is quieter but that’s still quite a difference. 

[JohnMo]

8 hours ago, G and J said:

get the idea that an oversized heat pump lasts longer and is quieter but that’s still quite a difference.

Sorry where do you get that idea. You can live with and make an oversized heat pump work, but the ideal is a correctly sized one. 

 

8 hours ago, G and J said:

Jeremy’s spreadsheet our not anywhere near

Its very close to reality on our house and our summer house.

 

11 hours ago, ChrisInKent said:

we’ve got a local plumber, who is working with us not against us

Good to hear.

[ChrisInKent]

9 hours ago, G and J said:

I’m thinking that either your numbers are wrong or mine are.  Using Jeremy’s spreadsheet our not anywhere near PH 150m2 design looks to need just over 2kW to maintain 20C when it’s -3.5C outside.  
 

I am assuming 87% MVHR efficiency and 0.5AC/h.  The air tightness and form factor (2.75) are the only PH ready things in the place really. 

I’m sure ASHP size will come down further once we have done the air tightness test and taken the plumber on the PH journey… he’s open to adapting the design once he understands the impact of MVHR AC/h, the other company wouldn’t.

[G and J]

53 minutes ago, JohnMo said:

 

 

9 hours ago, G and J said:

Jeremy’s spreadsheet our not anywhere near

It’s very close to reality on our house and our summer house.

That’s good to hear and I have assumed it was bang on, hence using it so much and relying on the output.  
 

So for our house, which is “not anywhere near” passive house insulation levels, Jeremy’s spreadsheet shows our heat loss at less than a third of @ChrisInKent’s.  Methinks if Jeremy’s spreadsheet is as good as I think then the 7kW is rather suspect.  
 

So Chris, why not give Jeremy’s spreadsheet a go?  

[JohnMo]

2 hours ago, G and J said:

Methinks if Jeremy’s spreadsheet is as good as I think then the 7kW is rather suspect

But as he says, until air losses are tested MCS will only use spreadsheets values equal to a very leaky house. Needs his air test certificate in hand first.

[G and J]

1 hour ago, JohnMo said:

But as he says, until air losses are tested MCS will only use spreadsheets values equal to a very leaky house. Needs his air test certificate in hand first.

So if the proscribed procedure is followed then I can’t finalise the design of the heating system including ASHP size until my build is proven airtight (or otherwise).  Crumbs.  I had assumed my airtight test would be done after screeding.