Radiator Placement and Eskimo Radiators

[PNAmble]

Hi, 

 

Whilst progressing groundworks, we are working on the heating design.  We are building based upon Passive House u-values and air-tightness (0.6)/cold bridging standards/MVHR;  the Thermal Model we initially commissioned has defined a Fabric Loss of 2.2Kw and infiltration/mvhr loss of 0.4Kw;  The Changeplan heat loss calculator (online) has matched the fabric loss but has calculated a very large 2Kw of Infiltration heat loss.  (both at minus 5)

 

The house will be an upside down house (living space has large south facing sliding doors with external blinds, master bed/ensuite on first floor all other bedrooms downstairs with north facing windows), for a variety of reasons the semi raft foundations will be Insulated / screed above.  For the former reason we have decided to heat via radiators/ASHP and not install UFH.  Using the Passivhaus advice that via radiators it should be planned to use approx 200% of the calculated heat loss, we've come up with a requirement for approximately 4.5Kw of space heating. (we have additional electric towel radiators in 3 bathrooms which aren't included in this calculation).

 

We want to run the ASHP at as low temperature we can (40/35 or even 35/40) using Weather Compensation (the heating engineer has identified a 5Kw Ecodan Monobloc ASHP), so radiator sizing is based upon the appropriate delta T correction factors.  

 

So the questions / advice I'm after is:

 

1) the theory in an airtight house is that all rooms will be the same temperature, following this does it really matter where the radiators are placed as long as the total output required is installed;  using the per room thermal model we've split the radiator output across ground floor and first floor as per the heat loss.

 

2) the correction factor applied to steel radiators means that we need to go for significant sized radiators; however, Eskimo Design has Aluminium Radiators (Column) (https://www.eskimodesign.co.uk/products/p/column) and they use a very different correction factor due to the design and use of aluminium which effectively makes them almost twice as efficient at low temperatures meaning we can use less radiators for the required output - meaning we save on wall space.   Has anyone used these radiators and do they operate as defined at low temperature.  We do understand that they will heat up quicker, and loose heat quicker than steel radiators but we don't think that's a problem in that we'll be running the ASHP continuously (as we don't have a concrete slab to heat up over night).  

 

3) Does anyone have a modulation curve of the ecodan ASHP, and will it modulate low enough during the "shoulder months" without cycling .. or to avoid this would we potentially "switch off" one of the radiators to lower the overall space heating installed output during these months. 

 

4) I assume that we don't need TRV's as the ASHP will modulate correctly, (we may have an overall thermostat to take advantage of the advanced load capability of the Ecodan ASHP). but is the assumption re TRV's correct.

 

We've had advice from our MEP consultants, but due to continuing errors in their work, and lack of responsiveness and general dislike of paying fees during the build we've disengaged their services, and we weren't convinced they really understood the impact of building an airtight house.  

 

Looking for advice and thoughts so that when we create our install plans for the MEP services they are correct.

 

Thanks in advance.

 

[HughF]

I’m questioning their claim of better heat transmission ….

[PNAmble]

Physics does support the idea. And where a heat pump is running 24x7 at low temp then the ‘retention’ of heat becomes a bit irrelevant ?   A little bit of knowledge is dangerous.  I have asked Eskimo and they are standing behind the correction factors.  

[S2D2]

Some random thoughts:

1. Would galvanic corrosion be an issue or is the PTFE sufficient?
2. They claim water content is 1/4 that of a comparable steel rad, which will make minimum system volumes harder to meet.
3. A 720x660 rad is £429+£40 postage?!

[Conor]

Have you completely ruled out UFH? At those prices for rads, UFH will be cheaper. You'll also not need to worry about wall space, and have much bigger water volume so the heatpump will work more efficiently. And you can take advantage of overnight tariffs.

 

We had a calculated loss of 3.5kW, and installed UFH in almost every room and powered by a 9kW heatpump. We normally only need to run it at 30c for 7 hours off peak, unless it's a proper cold snap. Wouldn't change a thing. We haven't bothered installing the three electric towel rads we bought as there is no need for them.

[PNAmble]

5 minutes ago, Conor said:

Have you completely ruled out UFH? At those prices for rads, UFH will be cheaper.

We have due to the upside down nature of the house.  We don’t have a thermal store in the foundations so the ‘load’ over night isn’t an option for us. 
 

Size of heat pump is the same as we are designing the radiators to run at 35 flow rate. 
 

interesting re the towel rails. How do you set towels ? Or so they dry naturally due to the MVHR? 

 

 

[PNAmble]

33 minutes ago, S2D2 said:

Some random thoughts:

1. Would galvanic corrosion be an issue or is the PTFE sufficient?
2. They claim water content is 1/4 that of a comparable steel rad, which will make minimum system volumes harder to meet.
3. A 720x660 rad is £429+£40 postage?!

1) aluminium rads have been about for years so I assume that’s not a problem

 

2) so this is a potential concern , not quite certain I understand the implications of min volumes.  How do they get worked out. And is the implication that I may need a buffer tank?

 

3) yes expensive but per corrected output wattage they are cheaper than many steel radiators (that would be used) and significantly smaller.  
 

 

[S2D2]

6 minutes ago, PNAmble said:

1) aluminium rads have been about for years so I assume that’s not a problem

 

2) so this is a potential concern , not quite certain I understand the implications of min volumes.  How do they get worked out. And is the implication that I may need a buffer tank?

 

3) yes expensive but per corrected output wattage they are cheaper than many steel radiators (that would be used) and significantly smaller.  
 

 

1. Indeed
2. Manufacturer of heat pump specifies them for defrost cycles. Solved with buffer/Volumiser on the return
3. Are you sure? If I use the site calculator it suggests I need 600*720@£677, comparable steel kudox premium T22 600x1200 @£80. Not comparing apples with apples from an aesthetics perspective, but that's a big jump. If you're set on the "designer" price tag then maybe not such a jump.

[PNAmble]

12 minutes ago, S2D2 said:

Are you sure

So agree there are cheaper solutions but actually your example isn’t like for like delta t 20 the Eskimo is 712w and your example Is 634w.  Due to the different correction values used by Eskimo (if it’s believable) which as you scale to bigger radiators especially tall as opposed to wide, the correction ratio and lightness of the radiators becomes a big factor is choosing radiators - looks are important as well.  
 

Thanks for the point 2 I’ll check to see if our design works as we hadn’t considered that. 

[S2D2]

Have you got a link to the correction calculation? The tool is rather crude hence giving me the "next size up". Interested in the height note as you will get a stack effect I guess.

[PNAmble]

24 minutes ago, S2D2 said:

Have you got a link to the correction calculation?

https://www.eskimodesign.co.uk/s/Correction-factors-based-on-Delta-T-50.xls

 

Our heating consultant who did the thermal modelling identified 5 (plus an optional 6th) radiators across the house (assuming house at 21 degrees steady state) to provide the output Using Eskimo we can reduce the size (they will all be 1800 high) and the delta t.  Hence why we are considering them from an aesthetics and HP CoP efficiency rating.
 

  

[Sparrowhawk]

They are beautiful radiators. If money was no object I'd fill my house with them.

 

I'd like some 3rd party verification of the correction factors though.

[ProDave]

If you have a calculated heat loss of 4.5kW and install a 5kW heat pump, it won't have any time to heat DHW.

 

+1 for UFH throughout.  Once you have had a house with UFH you won't want one with radiators again.

[S2D2]

It does seem to be a bit too good to be true on their stated outputs:

 

Kudox alulite 1800x280mm=702W(d50)

Eskimo column 1800x233mm=1522W(d50?)

 

Heat geek got caught out by this with his home rads, the stated output randomly used d65 on the website without specifying rather than d50, so all of his calcs were off. I suspect something similar is going on.

Edited September 25, 2023 by S2D2

[PNAmble]

12 minutes ago, S2D2 said:

I suspect something similar is going on

I have emailed Eskimo Technical Services who are assuring me that there is no error, I've followed up asking for any independent validation, they work closely with Birmingham Uni, so hopefully they'll have some independent data.   

[PNAmble]

29 minutes ago, ProDave said:

If you have a calculated heat loss of 4.5kW and install a 5kW heat pump, it won't have any time to heat DHW.

 

+1 for UFH throughout.  Once you have had a house with UFH you won't want one with radiators again.

 

I have lived in a house with UFH, and I don't want to install UFH in the guest rooms which are downstairs, and the master bedroom which is upstairs.  Which would lead me to only install UFH in the open plan living space upstairs and radiators in key positions downstairs (effectively the entrance hall and down stairs landing).  If we had a ground floor living arrangement and a slab then the discussion would be different.  The actual modelled heat loss is 2.4 Kw (at -5 / 21 with a ACPH of 0.6) which PH recommend a 200% uplift for radiators - although it's unclear why.  Our view which could be wrong or just optimistic is that: 

a) temperature is very rarely -5 so average worst case heat loss will be less (we are coastal and the temp file used is not accurate for our region)

b) we totally anticipate beating the ACPH hence reducing heat loss - we have planned on interim airtightness testing to help with this

c) stepping down heating at night to 19 provides an element of headroom 

d) for the few rare days in winter; boosting hot water via immersion heating using cheap rate/or PV electricity. (its only cold here when its clear skies, so PV will be able to trickle feed the hot water)

e) Heat Pumps need to be right sized and overspecifiying creates a problem with modulating and hence cycling as we aren't loading the "slab" at night, the heat pump even if we had UFH will effectively need to run 24x7 at low temperature. 

 

as I say we may be mad.