I should think that a heat loss calculation might be a wise first move; with good insulation in a modern building, you may well find you are looking at heat generation less than 50 kWh as at present, you are presumably kept warm enough with the 100 kWh system that’s probably no more than ~90 % efficient. As to GS versus AS, I would not like to comment as I have no experience for comparison; bear in mind that GS will involve extensive digging up of the ground to install the ‘slinkies’ or other pipework system. Good news about the real estate to cover with solar panels - go for it! The most expensive component for the solar may be energy storage of course. Regards, Toodles.

A few random thoughts:

1. Solar will mostly be produced in summer ... least when most needed. So should be seen as valuable resource for income but less for creating enough power for own use.

2. Batteries should be a priority if possible. Both to store own pv solar but also import on cheaper time of use tariffs. Inverter sizing and design will be important.

3. Rather than target a system that can fully heat on coldest days should you consider:

A) system that heats nicely in shoulder months plus winter down to (say) +5 daytime/ 0deg nighttime. Rather than go for a system that is sized for all seasons.

B) a secondary system that boosts in coldest weather. That could be an extra ashp or could even be gas/oil

4. Presumably requiring 3 phase power installed? At what cost?

@josephiah Hi, we just completed a Church but using air 2 air ASHP, total capacity 48kW, the reason we used A2A is so they have cooling in the summer as well as they said it tends to overheat once there is 200+ people in the summer. If you have a wet system, you want to use it and there is space at the back of the building then Mitsubishi Ecodan do a nice 45kW unit that is Air-Water but and just to give you an idea, if you have 54mm main pipework it will carry around 100kW but if you change this to a HP you will need to upgrade this to 80mm pipework to carry the sam 100kW (in actual fact I would imagine 100mm may even be needed) This will be expensive, there may be other work arounds. 

You could split the system and have 2 systems that would help with the pipework a bit, initially I would get a full heat loss assessment and start from there.

KR

Hi @josephiah, there's quite a good range of small commercial 3Ph electric heat pump units, or reversible chillers. Example: https://www.aircon.panasonic.eu/GB_en/news/new/panasonics-new-r290-air-to-water-reversible-heat-pumps-in-capacities-50-80-kw/

Many use R290 propane in packaged units with good part-load modulation. Consider a reversible heating and cooling unit so you can have UFH in winter for space heating, and can quickly boost supplement this with chilled water/warm water fan coil units. Fan coil units can provide space cooling in summer when the auditorium is full. GSHP trench loop or bore hole is going to add quite substantial civils costs over ASHP. GSHP offers better SCOP, but you need to consider the payback of a £30-40K additional cost [wet finger estimate!] for the civil works and additional plant for GSHP over ASHP.

I would strongly recommend you engage the services of a competent and experience building service engineer or company to get some concepts and budgets drawn up. https://www.cibse.org/directories/directory-of-practices/ You can't design this via this forum, via Google, or DIY. Well you could, but you know what I mean.... 😉 You'll need to pay for a feasibility and concept study and professional advice, but that will be money well spent in the right hands.

They'll consider the usage profile of the church, zoning - perhaps two heat pump, cascaded, one sized for the café & welfare facilities, and the auditorium on set back, and a second heat pump sized for the auditorium when occupied to give good turn-down and low load efficiency. They will review the existing system and how readily it can be converted from fired LPG boiler to heat pump space heating, maybe with heat pump space cooling.

Solar and BESS is a good way to offset your energy costs, especially if the church & café will be all-electric single energy. The problem churches have is that getting a feed-in-tariff to use surplus solar PV as an income stream can be difficult. Churches are classed [rightly or wrongly] as commercial/business premises and very few utility companies offer FITs to businesses.

@toodles - yes, I'm sure the actual heat requirement will be far less.  100kW is the absolute upper bound, but I'm expecting something around half of that or less.  

@tim441 - thanks, yes, all makes good sense, and is familiar from my domestic setup.  I think we have a 3 phase connection already, but it's high on my list of things to check.

@ashp-bobba & @allyfish - I like the idea of a twin system.  We're in the Highlands, so cooling is less of an issue - generally we just open a window!  But worth considering.  Much optioneering to be done - thanks for the helpful suggestions/pointers in terms of potential zoning splits and pipework, etc.  Early on the list along with the heat loss survey will be to dig out/survey the existing kit and see what's there.  We'll want to avoid digging up the existing underfloor loops, so first step might be to see what throughput that could be capable of with an ASHP, and then work out what type of top-up options would be possible, if needed.  GSHP probably not worth the additional cost/hassle by the sounds of it. And yes, certainly planning to get the professionals in - but want to be well armed going into those conversations.

Also going to be checking out what kinds of grants are available - CARES community funding looks like the obvious one in Scotland (up to £80k / 80% intervention), but current round applications close at end of October, all works done by end of Feb, which I think is just infeasible (my domestic export permission took longer than that, and I can't see getting buy-in for heating works over the winter!), so probably waiting to see what the next round looks like - unfortunately these things often get less generous over time...  Got a call with Local Energy Scotland tomorrow to see what they're saying...

On the solar side, from a quick look at the roof area available, we could get a 100kWp array up there fairly easily if we wanted to...

I wonder if this is a project @aventus-eco would be interested in… 

Posted by: @editor

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I wonder if this is a project @aventus-eco would be interested in… 

Church projects are never straightforward, very complex to work with. We are currently quoting for two at the moment. Yours, being more modern, sounds a lot easier than what we are dealing with just now.

The first one is in Aberdeen with a 150 kW heat loss. The end client does not want air to air and will not upgrade any of the existing emitters, so we have had to come up with some ingenious solutions. The second church is on the west coast. It is one large hall and we are planning to use the existing heating system to hold a setback temperature, with air to air being added as Bobby suggested. Both of these jobs are currently going through CARES funding.

I would be happy to come along in person, have a look, and speak with you directly. Where is the church located? This Saturday and Sunday I will also be at the Edinburgh Home Building and Renovation Show with a trade stand. Feel free to pop along and see me if you like. I should be able to email you over some free tickets through the show portal.

My email is info@aventuseco.com and my mobile is 07504685781.

Kind regards,
Sean

@aventus-eco Thanks Sean, will drop you a line.

I would look at the Panasonic R290 M series large units combined with their Smart fancoil radiators, so you can have low flow temps and high outputs and no water blending for your underfloor heating. The do up to 30kw

We install mostly A2A for churches and village halls, often due to little use and quick heating required. They will always work out substantially cheaper to install and control. If a decent wet system already in place then an A2W may also be a good option if the building is used frequently.

This church project has more in common with a commercial building than a home.  

Maybe an obvious point, but it is important to consider how quickly the main worship area can be heated up.  You might want it to be unheated throughout the week, but then be nice and warm for the Sunday morning service.  If you have mid-week services or conferences, then you need to heat the worship area in plenty of time.