Logical steps. Help!

[flanagaj]

I have become rather bewildered regarding what aspects I need to do and it what order.  The technical architect is currently doing the drawings for building regs submission and another company (UK building compliance) are doing the following.

L1A SAP 10 Calculations New Build (inc Design, As Built & EPC)Design Stage SAP L1A Assessments and PEAs
   a. Assessment under the 2021 Part L Building Regulations;

   b. Design Final Checklists for Building Control;

   c. Predicted Energy Assessments (PEAs);

   d. Thermal Bridging Calculation (y-value) based on Accredited Details (if used);

   e. Thermal Mass Parameter Calculation;

   f. Assistance with thermal, heating, lighting and renewable specification (including revisions);

   g. To include for unlimited specification revisions;

   h. Access to Dashpivot app for recording of photographic evidence.

 

As-Built SAP L1a Assessments and EPCs
  a. Assessment under the 2021 Part L Building Regulations;
  b. As-Built Final L1a Checklists for Building Control;
  c. BREL report;
  d. Verification of photographic evidence;
  e. Energy Performance Certificates (EPCs).1.00310.00310.00

Water Efficiency CalculationsPart G Water Efficiency Calculation/s, consumption to meet requirement of 125L (or less if required) per person per day. Includes PDF Report.1.0095.0095.00CIBSE TM59

Overheating AssessmentDetailed overheating assessment in accordance with CIBSE TM59. To demonstrate compliance with Part O Building Regulations 2021. To include for an appropriate sample requirement & x 1 re-run of the calculations

Do I need to wait for the details of this information, before I can start designing the UFH and ASHP?   I did put the details in Jeremy's spreadsheet, but I am bemused as to what order to do things.

Any pointers welcomed.

[SteamyTea]

2 minutes ago, flanagaj said:

Do I need to wait for the details of this information

Probably as it will help highlight mistakes.

If the people doing the calculations are unsure of anything, they will default to a worse case.

While you wait for the information, start doing your own research/calculations.

 

Think of it as marking their homework.

[flanagaj]

34 minutes ago, SteamyTea said:

Probably as it will help highlight mistakes.

If the people doing the calculations are unsure of anything, they will default to a worse case.

While you wait for the information, start doing your own research/calculations.

 

Think of it as marking their homework.

I have started doing my own research, but unsure whether it is correct or not.

[SteamyTea]

11 minutes ago, flanagaj said:

correct or not.

Ask here, sure it will get sorted 

[BotusBuild]

There is no harm in thinking about UFH manifolds placement, and how each loop would get to the one it needs to connect to (remember 2 pipe per loop when it gets to the manifold, leave room!)

Starting using LoopCad to form some ideas on where pipework will be.

For the MVHR, there are two main ducting systems, I refer to them as hard and soft. Hard ducting is unforgiving if something is built in the way of a route, difficult to put perpendicular to joists. Soft ducting (flexible, narrower pipes) actually needs a lot of room when you get to the manifolds (I know 😀).

So think about options where the main unit can go and how it would impact on ducting design.

Soil and waste pipe layout!! Discuss where all those sinks, basins, baths, showers and toilet etc. are going to go and don't forget possible plant room condensate and safety valve overflow pipes.

For showers, think shower trays, steps, wet room??? And then make sure the builders know so that waste pipes can be located accordingly (don't ask me how I know!)

HTH

 

[flanagaj]

So Jeremy's heat loss calculator gave me a 3.7Kw value.  I plugged these details into ChatGPT and it has come up with the below.  Anyone care to cast their eye over it and see if what it is suggesting looks correct.

 

Awesome—thanks for the room schedule. Here’s a crisp sizing plan that fits your 5 kW reversible ASHP, gives proper bedroom cooling with dehumidification, and uses UFH for gentle background cooling downstairs.

Bedroom cooling (use small hydronic fan coils)

Rule-of-thumb sensible loads in a well-insulated UK home:

• Standard beds: ~35–45 W/m²

• Master: ~40–50 W/m² (bigger volume/glazing)

Recommended FCU sensible capacities (at ~7/12 °C water, 27 °C room):

Room	Area	Est. sensible load	Suggested FCU
Master	30 m²	1.2–1.5 kW	~1.5 kW unit (quiet on low)
Bed 1	19 m²	0.7–0.9 kW	~1.0–1.2 kW unit
Bed 2	15 m²	0.6–0.8 kW	~0.8–1.0 kW unit
Bed 3	14 m²	0.5–0.7 kW	~0.8–1.0 kW unit

Notes

• Bedrooms are carpeted (good for heating comfort; irrelevant for FCU cooling).

• These small FCUs give you latent removal (dehumidification)—the key to comfortable sleep.

Downstairs cooling (UFH + optional 1 FCU)

Polished concrete is perfect for UFH cooling, but radiant floors don’t dehumidify and must stay above dew-point.

UFH cooling outputs you can bank on (safe, quiet):

• With supply ≥18–19 °C and typical UK indoor ~24 °C / 50–55% RH → ~20–35 W/m²

Expected background cooling from UFH:

• Kitchen-diner 35 m² → ~0.7–1.1 kW

• Lounge 19.5 m² → ~0.4–0.7 kW

• Downstairs UFH total: ~1.1–1.8 kW

Optional add-on for muggy days / solar gain:
1 discreet FCU in the kitchen-diner, ~1.5–2.0 kW sensible, to mop up humidity and peaks. (Highly recommended with big south glazing.)

Diversity vs your ~5 kW ASHP

• Likely coincident demand: Master + one small bedroom + some UFH ≈ 3–4 kW, which your 5 kW unit handles easily.

• Even with all bedrooms calling, fan speeds modulate and loads are rarely simultaneous at peak. The optional downstairs FCU can be limited by control if needed.

Control & safeguards (important)

• FCU loop: chilled water 7–12 °C, each FCU on a 2-port valve, own small circulator, proper condensate drains.

• UFH cooling loop: enforce dew-point control. Example: at 24 °C / 55% RH, dew point ≈ 15 °C → cap UFH supply at ≥17–19 °C (controller with RH/temperature input or dedicated dew-point sensor).

• Modes:

  • Heating: weather-comp 35–40 °C to UFH.

  • Cooling: FCUs on 7–12 °C; UFH at dew-point-safe setpoint.

  • DHW: priority reheat; weekly 60 °C pasteurisation.

DHW (2 occupants, occasional 6)

• Cylinder: 200–250 L, heat-pump coil ≥2 m².

• Recovery: 5 kW ASHP reheats 200–250 L (10→45 °C) in ~60–90 min. On guest days, schedule a mid-evening top-up.

Quick bill of materials (to brief installer)

• Reversible ~5 kW air-to-water ASHP, min modulation ≤1–1.5 kW.

• HP-ready 200–250 L cylinder, ≥2 m² coil, DHW priority + weekly pasteurisation.

• Bedroom FCUs: ~1.5 kW (Master), ~1.0–1.2 kW (Bed1), ~0.8–1.0 kW (Bed2), ~0.8–1.0 kW (Bed3).

• Downstairs: UFH cooling with dew-point protection (+ optional 1.5–2.0 kW FCU in kitchen-diner).

• Hydraulics: FCU chilled loop with own pump; UFH on mixing/limit control; 3-port diverter for DHW. Low-loss header only if flow stability demands it.

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If you want, I can translate this into specific FCU model sizes (wall/console or slim ducted) and a control sequence (setpoints, interlocks, sensors) tailored to your preferred brands.