Passivehaus / EnerPHit PLUS rating for generation

[joth]

Just got the first draft of our completed pre-construction PHPP  and I did a little happy dance on opening the PER tab:

 

What this says is our 8kW of self-generation (vertical axis normalized to ground floor footprint) is enough to offset our energy demand (horizontal axis, normalized to total inhabitable floor area) and achieve their new-ish "PH Plus" category.  So far there's only one in the UK that has achieved this (that I know of) so exciting times ahead! (if all rather arbitrary I'll admit, sure).

 

Anyone else gone through PHPP and got PER charts for comparison? 

 

 

 

 

Edited August 2, 2019 by joth

[Dan F]

@joth We'll be somewhere around there, depending on thermal bridge calcs, efficiency of ASHP and amount of PV.

 

Unsure how much sense it makes to try to explicitly to meet PH Plus standard though, we'll see. (We will be certifying though)

 

Do you now have the construction numbers? Are they along the same lines? Timber frame? Are you certifying?

 

Think there are 4-5 in U.K now for what its worse..

 

Dan

Edited December 30, 2019 by Dan Feist

[joth]

@Dan Feist great stuff! Where abouts are you in the country?

Our construction starts January 7 so no actual figures just yet. Soon! So very soon. (move out in 3 days time.... So soon)

 

Existing is block and brink, new parts will be timber. It's an interesting house being a 60s cross wall construction, we actually demolishing the two external non-load bearing walls to rebuild in place to a higher spec. Not sure anyone has attempted this before (for passive house reasons)

 

Yes, will be certifying.

 

To confirm, there's 4-5 enerphit Plus now (i.e. retrofits)?. I thought there's only one (the Manchester pair of semis) but maybe out of date. I can imagine, like everything else, achieving it on a new build would be much simpler as you can design everything around the microgeneration. We have to deal with the aspect and roof pitch we inherited.

Edited December 30, 2019 by joth

[Dan F]

We're in Berkshire. We are demolishing in next couple of weeks and laying foundations in March if everything goes to plan.  We did design phase PHPP and have now updated it based on tweaked layout, window sizes and window spec, but we're waiting on the timber-frame design before exact u-value and thermal bridge details can be completed.  We should get TF design in the next couple of weeks.  Tree shading and thermal bridges both have a significant impact on PHPP numbers so need to wait for TF company to TF design, and get input from cetifier on trees before we can be confident..

 

Sorry I mis-read, you are correct it seems there jus one "enerphit plus", 4-5 new builds.

 

We're not targetting plus explicitly and haven't designed anything around this. In fact, because we have a stepped design, our "projected area" is farily high compared to the actual roof space available for PV.  We are planning i) ASHP ii) decent amount of PV anyway though, so if getting a more efficient (R32 or R290) ASHP  and/or using 330/350W instead of 300W panels gets us there and there are also longer-term cost benefits, we might hit it..

 

 

Edited December 30, 2019 by Dan Feist

[joth]

Yes, by no means will all Passivhaus builds automatically be plus rated, but I can see if someone is setting out for plus rating it will be easier to get it on a new build vs a retrofit, hence my assumption there are very few retrofit pluses out there.

That said we definitely didn't set out with it as a goal either. Just our roof lends itself to a full pitch of PV and it actually made the planning application simpler in some ways. 

 

I actually found several "bugs" in out PHPP since the chart above was made, which puts us more comfortably inside the Plus loci (lower demand; further left). I'll dig out the details tomorrow, but heating system temperature and the heuristic for circulation pump wattage (!) was a large part of it. 

[Dan F]

1 minute ago, joth said:

I actually found several "bugs" in out PHPP since the chart above was made, which puts us more comfortably inside the Plus loci (lower demand; further left). I'll dig out the details tomorrow, but heating system temperature and the heuristic for circulation pump wattage (!) was a large part of it. 

 

Are you doing the modelling yourself?  We're using someone else, but I have the PHPP (read-only) and it's great fun playing with all the variables ?

 

Be interesting to see what bugs you found, I've noticed that the PER calculation includes a lot more inputs than the basic "heating demand" calcuation and length of pipes, UFH supply temp, size of UVC etc all start to have an impact..

 

 

[joth]

My architect is doing the PHPP, she's a certified passive house designer, we're her first project, so it's a little bit of a voyage of discovery on both sides but working out really well as our respective backgrounds complement each other well (me more on electrics and, at a push, plumbing, her on the building design and fabric build up etc)

I had the M&E co provide initial figures for the pipework etc

I've really enjoyed having the PHPP file to use as a tool to see how it works in different  scenarios and comparing ASHP performances etc,  and indeed this was where I discovered the issues in plumbing figures:

(i) First thing was getting the HP tab to correctly have single pump do heating + DHW -- for whatever reason, it only does this if the DHW+Distro tab has a correctly configured buffer tank.

(ii) Then I needed to get the design temp down from 70ºC to 35 (update as we're no longer planning fan coil upstairs, at least initially).

(ii) Then the AuxElectricity went through the roof, as for reasons I can't fathom it has a heuristic that the circulation pump power is a function of the system design temp. At 70ºC it estimates they'll draw 50W but at 35ºC it suddenly reckons they'll need 110W each. Combined with the fact we have 3 circulation pumps and it reckons they'll all run 20 hours a day, 212 days a year, and this totally dominates the PER demand (and offsetting the ASHP heating demand; a significant of the home heating is provided by the motors in the circ pumps themselves at that wattage). I just proposed an override of 40W for the pumps, as that seems more than generous enough based on examples I can find.

 

With all that in place, this is the updated chart: generation is still a snag below the "target" dot, but our demand is much lowered making it on track for nicely inside the Plus area. Of course, achieving this in practice will be another matter.

 

Edited December 31, 2019 by joth

[Dan F]

The heat pump looks fine in ours (fairly standard spec one currenlty only though).  I can't see any circulation pumps though, unless they haven't been added.  Other thing like the length of DHW pipes can also have a suprising impact!

 

@joth Can I ask how you (or your designer/certifier) have dealt with tree shading.  Tree shading has a huge impact on numbers but modelling them correclty is impossible and it's seems it's mostly rough approximation. Until our designer/certifier agree on the tree shading, we don't really know where we are...

Edited January 1, 2020 by Dan Feist

[Dreadnaught]

@Dan Feist, just checking that you know that Peter Warm developed an additional sheet for PHPP 9 for shading? It adds certain extra functionality which improves to some extent the basic shading controls, which are helpful if your site is tree-shaded.

 

I used it in 2018 for my modelling and corresponded briefly with Peter about it then.

 

Peter Warm's notes on the sheet: "An add-in sheet for PHPP 9, which allows you to easily model shading objects that are discontinuous and/or which have transparency. These include trees, tower blocks, brise-soleils, juliet balconies and plant-on glazing bars."

 

Here is a link to download the additional sheet: http://www.peterwarm.co.uk/?dl_id=52

[Dan F]

@Dreadnaught I did come across that yes, although it does say "deprecated" now, not sure why.

 

This sheet has been useful for my own modelling of trees, even there is a fair amout of guesswork though given:

- It's hard to estimate the transparency of trees.

- Multiple trees can impact a window and not just the tree (if any) in a perpendicual line from the window.

 

The other thing that's somewhat guesswork if the size of reveals.  We have a south-facing house with a breakfast room projecting from the back and a westerly 3m patio door out of the breakfast room onto a patio.  This patio door technically has a 5m reveal on both sizes (average of 0m and 10m), when in fact the 10m reveal (the back of the rest of the house) is north facing and not going to shade at all.

 

Anyway, for us, given we are certifying, we're just going to have to wait and see what designer/certifier agree on and then see where we stand..

 

Thanks!

[joth]

15 hours ago, Dan Feist said:

@joth Can I ask how you (or your designer/certifier) have dealt with tree shading.  Tree shading has a huge impact on numbers but modelling them correclty is impossible and it's seems it's mostly rough approximation. Until our designer/certifier agree on the tree shading, we don't really know where we are...

 

To be honest I know very little about this. The designer did it, the certifier agreed with it, that's all I know. From the small play I did have it didn't seem to have so much effect for us. Being a retrofit we don't  have any due-south windows, and minimal opportunities to alter existing windows, which may be part of it.

It was a bit disappointing the Solar PV tab in PHPP required the shading to be done all over again, and of course our solar contractor has to do it again too (for MCS and for deciding how much per-panel Optimizers will be), so it's a often repeated inaccurate science! I recall one of the PHPP books says something like "it's really hard, in fact basically impossible, to get it perfectly right, so just do the best you can" or words to that effect. Alas I can't refer to any books as they're all packed. (Moving out tomorrow!)

(Even if you could get the shading perfectly right, someone can cut down a tree of put in a new one tomorrow anyway... so it's impossible to correctly model over the lifetime of the house).

 

 

[Dan F]

Exactly, our design-phase modelling explicitly didn't even include trees for this very reason!  But for certification, we can't have no trees...

 

Good luck with the move!!

[joth]

On 02/01/2020 at 13:27, joth said:

I recall one of the PHPP books says something like "it's really hard, in fact basically impossible, to get it perfectly right, so just do the best you can" or words to that effect. Alas I can't refer to any books as they're all packed.

It may have been Peter Warm's blog actually:

http://www.peterwarm.co.uk/10-most-common-phpp-mistakes/