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  • Cost of having hot water on tap. Heat pumps no good, heat the water you

    From Dave@21:1/5 to All on Sat Mar 25 12:30:28 2023
    XPost: sci.physics, alt.sci.physics, uk.politics.misc

    Looking at the need for heat pumps as government recommended in GB,
    which is wet radiator heating and a hot water tank.

    My hot water tank which has so much insulation it loses next to no heat,
    except back through the three way valve and the boiler circuit needs
    about 1.5kWh/day to keep the temperature usable and high enough to be
    safe (min 50C). So in a year it is 365*1.5 or 547kWh/year to be able to
    run a hot tap on demand. Of course the setup is so bad the temperure is
    lowered by the cold coming in as soon as you use any hot, so you need to
    heat it soon after. This is not included in the 547kWh/year. With
    electricity this is about GBP 200 for nothing but a standby (GBP 0.35/kWh)

    Assume 2 people use 40l of 40C /day from the tank. Showers heat their
    own water, the washing machine and the dish washer heats its own water.
    The energy needed per day with resistive heating, assuming 12C input is:
    Heat capacity is 4.2J/g/C

    (40-12)*4.2*40*1000 is 4.7 MJ/day. or 4.7/3.6 or 1.3 kWh/ day.

    So over half the water heating cost is from having it on tap. A heat
    pump is not the right solution for this. Need water heaters at each
    sink with timers, with next to no storage.

    Of course care homes, hotels and district heating can benefit from the
    scale. Can't justify a GBP 15,000 cost + GBP 400/year maintenance for
    heat pump water heating for an average house.

    Well managed resistive heating does the business for most people with
    lower energy use and lower install cost. If you want a bath every day,
    then that's a different issue.

    About 1990 combi gas boilers came in to avoid the need to store hot
    water, and now heat pumps are bringing the hot water tank back.

    The UK government is trying to force people in GB to have heat pumps,
    but the physics doesn't work out good with the economics for most
    people. This is where tech gets interesting - legal, regulation and
    politics boundary - also the conspiracy to ensure the heat pump
    companies and maintence people grow their business at your expense. This
    is the basics of physics which affects society for decades to come.
    Media tends to concentrate of irrelevant particle physics and cosmology.

    Heat pump heaters with air output which are also air conditioners are appreciated on 100F / 40C days.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Jim Pennino@21:1/5 to Dave on Sat Mar 25 07:07:00 2023
    XPost: sci.physics, alt.sci.physics, uk.politics.misc

    In sci.physics Dave <[email protected]> wrote:
    Looking at the need for heat pumps as government recommended in GB,
    which is wet radiator heating and a hot water tank.

    My hot water tank which has so much insulation it loses next to no heat, except back through the three way valve and the boiler circuit needs
    about 1.5kWh/day to keep the temperature usable and high enough to be
    safe (min 50C). So in a year it is 365*1.5 or 547kWh/year to be able to
    run a hot tap on demand. Of course the setup is so bad the temperure is lowered by the cold coming in as soon as you use any hot, so you need to
    heat it soon after. This is not included in the 547kWh/year. With electricity this is about GBP 200 for nothing but a standby (GBP 0.35/kWh)

    Assume 2 people use 40l of 40C /day from the tank. Showers heat their
    own water, the washing machine and the dish washer heats its own water.
    The energy needed per day with resistive heating, assuming 12C input is:
    Heat capacity is 4.2J/g/C

    (40-12)*4.2*40*1000 is 4.7 MJ/day. or 4.7/3.6 or 1.3 kWh/ day.

    So over half the water heating cost is from having it on tap. A heat
    pump is not the right solution for this. Need water heaters at each
    sink with timers, with next to no storage.

    Such was invented many decades ago and are called flash heaters, though
    the don't have timers and only heat on demand.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)