navitron
 
Renewable Energy and Sustainability Forum
Welcome, Guest. Please login or register.

Login with username, password and session length
News: Anyone wishing to register as a new member on the forum is strongly recommended to use a "proper" email address - following recent spam/hack attempts on the forum, all security is set to "high", and "disposable" email addresses like Gmail, Yahoo and Hotmail tend to be viewed with suspicion, and the application rejected if there is any doubt whatsoever
 
Recent Articles: Navitron Partners With Solax to Help Create A More Sustainable Future | Navitron Calls for Increased Carbon Footprint Reduction In Light of Earth Overshoot Day | A plea from The David School - Issue 18
   Home   Help Search Login Register  
Pages: [1]   Go Down
  Print  
Author Topic: Best of the worst oil fired water heating.  (Read 2018 times)
todthedog
Global Moderator
Hero Member
*****
Offline Offline

Posts: 4235



« on: August 21, 2019, 03:50:57 PM »

All our neighbours  including ourselves have modernish oil condensing boilers for hot water and central heating, everyone then gets together early Autumn to bulk buy oil for the best rate. Apart from hand washing (we have an instant electric shower) so are a bit out of this conversation. However the question came up, are you better having the boiler up high to heat the water hot for a couple of hours night and morning and then off the rest of the time or on for longer and heat to a lower temperature?


I believe that condensing boilers work more efficiently at lower temperatures, but could be wrong.

Any thoughts?
Logged

'In a time of universal deceit, telling the truth is a revolutionary act'
Countrypaul
Hero Member
*****
Offline Offline

Posts: 1486


« Reply #1 on: August 21, 2019, 04:22:45 PM »

I suspect the answer will vary from house to house. If there is a family and the kids have a bath before bedtime with everyone out of the house during the day then having the water heated twice a day might make sense. The hotter the tank of water is the faster it will lose heat, so heating the water up high and leaving it for most of the day will result in loss of heat anyway. If there is only you and you have a shower in the morning and then leave it all day unused other than using a little in the evening, your usage would be obviously very different. If you were a couple working from home and using hot water all day at various times then again a totally different usage profile.

If the boiler is only heating the water and no providing the central heating then the overheads of the oil boiler might be more than you realise. If it takes 1/2 an hour to heat up the hot water tank and the boiler uses 2L/hr than that would be 10kWh of heat used. How much would be used to actually heat the water - an immersion heater might actually be more efficient and environmentally friendly.
I found this with our old house, where the boiler would run for 1/2 hour to get the HW up to temperature, but running the immersion heater for 1/2 achieved the same. 10kWh vs 1.5kWh and much lower CO2 output even if it was from coal power stations!

I too have read that condensing boilers work more efficiently at lower temperature where they can condense the water out of the exhaust. In most cases I have seen mentioned that the return flow needs to be under 55C - which is obviously not relevant if only using it for DHW though.  I don't know whether a condensing boiler can still condense when heating up cold water - I can't see why not though, but at what temperature will it stop?
Logged
myozone
Sr. Member
****
Offline Offline

Posts: 294


Lizard peninsula - Cornwall


« Reply #2 on: August 21, 2019, 06:55:50 PM »

What I do (2 person household) is have the boiler come on twice a day around breakfast time and lunch time for a few minutes. The boiler has a small 'thermal store' of 69 Lts I think in it, so only takes a few minutes to heat up with 25Kw. The rest on the time the water is still hot via the circulation pump and heat exchanger and the thermal store - 8.5Kw electric shower.
« Last Edit: August 21, 2019, 07:01:48 PM by myozone » Logged

'Don't live life by the perforations' !
ecogeorge
Hero Member
*****
Offline Offline

Posts: 1323


« Reply #3 on: August 21, 2019, 10:01:55 PM »

Not gonna be popular saying it ..........BUT
shame on you all heating DHW with oil ............
2 person household here  , 210 litre hot water tank , 2kw pv , tiny wood burner with 1kw to water back boiler.
Boosted water with mains electric less than 5 times this year .
All heated by wood (scrap pallets) or surplus pv.........
And yes we shower daily , dishwasher plumbed into hot.........
George
Logged
brackwell
Hero Member
*****
Offline Offline

Posts: 3031


« Reply #4 on: August 22, 2019, 08:25:08 AM »

A boiler of any type heating a tank of hot water particularly when the CH is not on is about as inefficient as it gets when measuring energy in v energy out.  The efficiency is likely to be 40% and even 35% if one does not understand things.  This is due to start/stop losses of the boiler, tank losses,dead leg losses. 
Just in time is what is needed and suggest a instant electric shower unless one has PV.  This is far more efficient energy wise and less when compared to oil.  If you want baths then perhaps the boiler is cheaper but uses more energy and pollutes (compared to RE/clean produced leccy)

Talking about heating at low or high temp is tinkering whilst Rome burns.
Logged
myozone
Sr. Member
****
Offline Offline

Posts: 294


Lizard peninsula - Cornwall


« Reply #5 on: August 22, 2019, 08:36:15 AM »

Quote
This is due to start/stop losses of the boiler, tank losses,dead leg losses.  

My timings are so short the boiler only runs once <7 minutes.  

Just looked at my HW timings 08:15-08:30 13:22-13:30
« Last Edit: August 22, 2019, 08:42:17 AM by myozone » Logged

'Don't live life by the perforations' !
todthedog
Global Moderator
Hero Member
*****
Offline Offline

Posts: 4235



« Reply #6 on: August 22, 2019, 09:01:13 AM »

Thanks for the thoughts chaps.

Wood burner not an option, no chimney for us. Our neighbours use a combo oil ch and additional heat from wood during the winter not all have chimneys. We have installed PV and a ashp heat pump which should provide heat for most of the year. We all do use oil for hot water.
We  are  thinking about instant water heater for the kitchen instant shower already installed.

 Neighbours  vary from retired singletons, to young families. For the young it is not an option for the retired  how hot and how long is a concern not wanting to have it on more than necessary particularly in the Summer. Also no big tanks where immersion heaters could be fitted, just small tank attached to the boiler.

Good to hear that lower temperatures are more efficient .



« Last Edit: August 22, 2019, 11:25:33 AM by todthedog » Logged

'In a time of universal deceit, telling the truth is a revolutionary act'
Iain
Hero Member
*****
Offline Offline

Posts: 1721


« Reply #7 on: August 22, 2019, 09:04:47 AM »

Hi
I know this is about oil but on my system gas boiler I have the hot water set to 45 deg. This is hot enough for use and also keeps the boiler in condensing mode. When I chose my boiler one of the things I looked at was how low it would modulate to. In order to reduce cycling. Works a treat.

Not sure how low an oil boiler will modulate to and also is the target temp set higher than needed?

Iain
Logged

1.98kWp PV (11 x Sharp 180 and SB 2.5)
20 x 65mm Thermal and 180ltr unvented
Powervault 4Kw - G200 Lithium-Ion (LiFePO4)
9000ltr rainwater storage   Plymouth
myozone
Sr. Member
****
Offline Offline

Posts: 294


Lizard peninsula - Cornwall


« Reply #8 on: August 22, 2019, 09:18:51 AM »

Quote
Not sure how low an oil boiler will modulate to and also is the target temp set higher than needed?

As far as I know domestic oil boilers don't modulate only large industrial ones ..
Logged

'Don't live life by the perforations' !
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.20 | SMF © 2013, Simple Machines
SMFAds for Free Forums
Simple Audio Video Embedder
Valid XHTML 1.0! Valid CSS!