Help, need advice for ashp

pennypuppy

Hello we have built a new house (no choice, last one falling down) and it's airtight and highly insulated. We were supposed to put an ashp in but we have run out of money and don't get a grant. Also have heard a lot of horror stories about crazy electric bills. So plan is to plumb it for an ashp but put on for a few years and oil burner. But what would we need? I know big radiators upstairs, downstairs is underfloor heating. Presumably we will need to either put in a hot water cylinder or leave room for it. Plumber heavily recommends puting in a condenser boiler for now. 

pennypuppy

Sorry so my question is what do we need to make sure the plumber does to make it ashp ready? 

matelodave

If you want hot water from a heatpump you need a hot water tank. |So if your intention is to make the place heatpump ready then you may as well fit it in the first place rather than trying to retrofit it in the future.

IMO faffing a round with an oil boiler (I'm assuming that you are confusing a condensing boiler - which all oil and gas boilers are, with a combination boiler - which doesn't  have a  tank) will just add extra cost and aggro, both to fit it in the first place and then at a later date to get it all removed.

Even worse if you go for a combi then you'll need to get the plumbing sorted to add a tank if you decide to fit a heatpump in the future..

When we fitted our heatpump in 2010 the incremental cost of a heat pump over and above the cost of an oil boiler and all its gubbins (tank, pipework, concrete base etc) wasn't really all that great considering that the rest of the system was the same.

Entirely up to you of course but do the sums.

A properly installed heatpump used correctly should be able to achieve a SCOP of three or more which brings the cost of energy roughly in line with that of gas or oil and the big advantage over oil is the fact that you dont have a ginormous tank in the garden and you dont have to worry about getting oil delivered, running out or getting it nicked.

FreeBear

matelodave said:

If you want hot water from a heatpump you need a hot water tank. |So if your intention is to make the place heatpump ready then you may as well fit it in the first place rather than trying to retrofit it in the future.

The cylinders used in conjunction with heat pumps are pretty large, especially if they have an integral buffer tank. You'll want a cupboard around 800mm to 1000mm deep/wide, and it needs to be fairly close to where a HP would be situated - Been looking at the specs for the Daikin ASHP, and it is limited to 10m of pipe to the tank.

On the subject of pipes - Main feed & return to the radiators needs to be a minimum of 22mm, and possibly as large as 28mm (or even 32mm) depending on the number/size of the radiators. 15mm is fine for short runs to the radiators. When sizing radiators, the calculations need to be based on a flow temperature of 35°C or a ΔT15°C. Unless you can get a modulating oil boiler (they do exist), I have a feeling that one might struggle with such a low flow temperature.

When you price up the cost of an oil boiler plus fuel tank, you will find that an ASHP will be very competitively priced. As an example, City Plumbing do a Samsung 8kW ASHP for £2083 (inc.VAT) where as a Grant oil boiler will be around £2000. On top of that, you'll need a fuel tank & flue (say another £1500).

If you have mains gas in the area, a gas boiler could be had for under £1000, but you'd still need to spend another £1200 or more to get connected. Or lease an LPG tank and get tied in to a supply contract with no option to shop around.

Netexporter

If the house is well insulated you won't need a very large heat pump. You can probably buy one for less than the cost of a new oil boiler and oil tank. Look on Ebay for a secondhand one.

The main thing is to get the heat loss and design calculations done properly for a heat pump. That will ensure it works efficiently and cheaply. It might work out cheaper (and definitely more efficient and comfortable) to design for underfloor heating. You could do most of the installation of the heating pipes yourself, rather than paying for a plumber to do a traditional central heating system. As others have said, the hot water cylinder will be quite expensive, on the other hand many of them are pre-plumbed, with all the pumps and controls incorporated, so you only have to plonk it where you want it and connect incoming/outgoing pipes.

Reed_Richards

If you put in a hot water cylinder make sure it is one suitable for use with a heat pump.  It will have a much larger surface area coil than a standard cylinder.  And remember that oil tanks are expensive and getting rid of an unwanted oil tank could also be expensive.

tacpot12

A Newark Heat Geek (HG) cylinder would be best: The HG Series - Designed by Heat Geek - Newark Cylinders

You can see the technical details of why this cylinder is particularly efficient here: https://youtu.be/uFBbArwAXS8