SimonD

Well, perfect timing. If you pop over to the tool I've developed at https://openheatloss.com you can model irregular shaped rooms (by breaking the room into segments) and each segment can use single or double pitched ceilings - it's text based, so you don't have to try and draw it. It's also open source and free so no need to upgrade your subscription.

I recently completed a design on a 1930s retrofit with cellulose insulation added to the suspended timbers floors and the ground floor U-values in that are between 29-36W/m2. The whole house average is 36W/m2.

I might actually have some pictures of the last one somewhere, but recently I was at my sister's place and she asked if I wanted my water level back, and forgot to bring it home. Next time I'm over I'll pick it up. I remember when I lent it to her, the builders and trades she was using (who couldn't work out how to get the levels right on part of her building work) told her it would never work. She demonstrated it to them and low and behold, they used it, amazed at how well this old fangled technology works. It drives me to despair when I hear this sort of stuff.

I hope the UFH design has not just been drawn up to a standard 40w/m across the whole house and has actually taken into consideration the room-by-room losses, designing according to those? Also 40W/m2 seems quite high to be for an energy efficient build.

It also depends on the diameter and length of the containers at each each. When I made my own, I found it was always best to have a large open container that's set to reference height and then use the pipe itself fixed to a batten with markers for the measurement side. There's also the the type and material of actual pipe. Some pipe I bought actually messed up the measurement as under the weight of the water contents and heat the walls would soften and change the content volume which could upset things and require a recalibration. The softness of the walls also lead to oscillation of the water level. Length does play a role due to resistance which can delay response time if you're climbing around on site with it. The best pipe I found was clear braided air-line tube and it could then be as long as needs and would also never kink. It feels a little sad that I know all this but I've made a few of these now!

Of course it's not sensible. It's also unrealistic. The EPC assessor actually has relatively little choice as it's the reduced SAP so simplified and based on lots of assumptions, and of course, it's actually fairly reasonable for an assessor to have to make assumptions without invasive investigations. The EPC is cheap too, so the expectations that a fee of less than £100 is going to give you something that's really accurate is a bit like expecting an accurate air permeability measurement for £50 quid with someone licking their finger and sticking it in the air) instead of a blower or pulse test. And one of the reasons why they're so conservative is partly because I bet a lot of customers ask them to inflate the report so they benefit from it. But this isn't with an EPC assessor, rather it's for someone actually doing the fully SAP?

It's not really about having the volume to satisfy flow requirements. The volume is to take the heat input from the heat pump and deliver it where it's needed. That's the beginning of working out your volume requirements. From a design perspective this is the start. Glad to hear chat gpt agrees on your design. The addition of a pipe temp sensor and valve with a pcb isn't really complicated at all because you've got to run all the cabling back to the Panasonic unit you've selected. By the time you've wired up another stat, zone valve, and a wiring centre, you might as well have just integrated it into the heat pump unit itself. This gives you more flexibility should you experience a control problem once it's up and running. Once you separate controls away from the heat pump, you're actually adding complexity plus additional control demands on you. You're potentially causing an additional rod for your own back. If the system design has been done correctly. I'm assuming someone sensible has done this and actually designed to ufh loops to room heat loads as opposed to provide a standard geometric exercise trying to fit pipes into the space to 150mm spacing, then simply running the whole system open on weather comp should be all you need. TBH, my alarm bells are ringing as you wouldn't believe the rubbish I see that's a result of a customer getting their builder and plumber to put in the UFH and then ask another person to install the heat pump. Usually they haven't got a clue on the UFH design or they farm it out to a UFH company that apply no sense to matching the design to the room demand. This is where you need to go back to before trying to figure out your control strategy. Are you having to put this in due to poor system sizing design in the first place? If so, then go with the manufacturer options because then you can move away from relay control to electronic mixers with separate curves to balance the heat across the manifolds if you need to, ideally controlled from the heat pump.

There's hardly any price difference between the two and often I find in bulk I get a better price with the MLCP pipe. The 'overkill' on something so basic when it's a totally unnecessary comment is weird. Personally I'd be going the route of MLCP at the drop of a hat.

Yeah, I'm clearly a bit naive and wet behind the ears on this 😁 Problem is trying to find one, just like trying to find any decent trades.

Agreed. I had an EPC done for my house and the assessor wouldn't include floor insulation and a few other things in his assessment. I got some amendments after sending photos of the work to prove the insulation was in there. But in the end we ended up 1 point below a B in energy efficiency, which is a complete joke. One of my customer got an EPC for the BUS Grant eligibility and also got a C, only a few points below us and half their house isn't even insulated but has solid wall. A big problem is that the price of an EPC is less than £100 - and that's to cover a full house survey, measurement and then a report? There's no way you can get this accurate with a quick 1 hour visit.

Honestly, I haven't been brave enough to give it access and control of my system and docs. If I set up a dedicated machine, I might do that. But yeah, it's amazing. This morning I was working through a problem and within 25 minutes I've got a working app that does exactly what I need it to do and I've haven't touched a single piece of code, job done. But I'm still surprise you haven't had to touch anything. I've still got to roll up my sleeves every now and again but maybe that's because I'm restricting access?

The promise is to use a different cold bridging methodology, probably using FEA tools, so yes a lot of work required, but better than blanket defaults as per SAP currently? If used correctly..... But this is interesting, because there is no mention of using BS EN 12831-1:2017 which is the UK standard for designing the space heating load. And this standard has only just been implemented. I wonder if this is going to lead to different standards being used for new builds using HEM that aren't necessarily going to be consistent with BS EN 12831-1. Or is there going to be another poorly considered change to the industry.

Sadly, the implementation probably will be.

The Future is HEM - https://home-energy-model.co.uk/

Is this timber frame wall a load bearing wall or is it just internal framing? If it's load bearing then you really want to follow standard timber framing methods. I would almost always use the 3rd option from left, but sometimes use option 1 if short of cls.