Gfrktyl

I wish to essentially remake the below image using TikZ, but with more colors and using a different language inside the boxes.

I've tried the following:

documentclass[tikz]{standalone}



  usepackage{mathtools}

    usetikzlibrary{shapes,arrows}

    % Define block styles

      tikzstyle{HOTRES} = [rectangle, draw, fill=red!20, 

      text width=20em, text centered, rounded corners, minimum height=1.5em]

      tikzstyle{COLDRES} = [rectangle, draw, fill=blue!20, 

      text width=20em, text centered, rounded corners, minimum height=1.5em]

      tikzstyle{line} = [draw, -latex']

      tikzstyle{cloud} = [draw, ellipse,fill=yellow!20, node distance=3cm,

      minimum height=4em]



begin{document}

    begin{tikzpicture}



    % Reservoirs

    node [HOTRES] (HOT)  at (0,2) {Kuuma};

    node [COLDRES] (COLD) at (0,-2) {Kylmä};



    % Heat transfer

    node [cloud] (HOT->COLD) at (-2,0) {(Q)};

    node [cloud] (COLD->HOT) at (2,0) {(Q)};



    % Lines

    draw [line] (HOT) -- (HOT->COLD) -- (COLD);

    draw [line] (COLD) -- (COLD->HOT) -- (HOT);



  end{tikzpicture}

end{document}

which produces this picture:

I just don't know how to achieve the effect of having arrows (that can just be simple TikZ arrows) leaving and entering the same node at different points, so that all of the arrows in the last picture were vertical. How could I achieve this effect with relative ease?

It is very simple, if you use the coordinate (nodea -| nodeb) you have the y coordinate of nodea and the x coordinate of nodeb.

Off-topic: see also Should tikzset or tikzstyle be used to define TikZ styles?.

documentclass[tikz]{standalone}



  usepackage{mathtools}

    usetikzlibrary{shapes,arrows.meta}

    % Define block styles

    tikzset{

        HOTRES/.style={

            rectangle, draw,     fill=red!20, 

            text width=20em, text centered, rounded corners, minimum height=1.5em

            },

        COLDRES/.style ={

            rectangle, draw, fill=blue!20, text width=20em, text centered, rounded corners, minimum height=1.5em

            },

        line/.style = {draw, -Latex},

        cloud/.style = {

            draw, ellipse,fill=yellow!20, node distance=3cm,

            minimum height=4em

            }

      }



begin{document}

    begin{tikzpicture}



    % Reservoirs

    node [HOTRES] (HOT)  at (0,2) {Kuuma};

    node [COLDRES] (COLD) at (0,-2) {Kylmä};



    % Heat transfer

    node [cloud] (HOT->COLD) at (-2,0) {(Q)};

    node [cloud] (COLD->HOT) at (2,0) {(Q)};



    % Lines

    draw (HOT.south -| HOT->COLD) -- (HOT->COLD.north);

    draw [line] (HOT->COLD) -- (COLD.north -| HOT->COLD);

    draw (COLD.north -| COLD->HOT) -- (COLD->HOT);

    draw [line] (COLD->HOT) -- (HOT.south -| COLD->HOT);

  end{tikzpicture}

end{document}

documentclass[border = 5pt]{standalone}



usepackage{tikz}

usetikzlibrary{calc}

usetikzlibrary{positioning}

usetikzlibrary{shadows.blur}



begin{document}

begin{tikzpicture}[

  reserv/.style = {

    draw = #1, fill = #1!50, text = white,

    rounded corners = 5pt,

    minimum width = 6cm,

    minimum height = 1cm, inner sep = 1pt,

    drop shadow

    },

  proc/.style = {

    draw = #1, fill = #1!50, text = black,

    circle,

    minimum size = 1.5cm,

    drop shadow, inner sep = 1pt,

    },

  arrow/.style = {

    line width = 1mm, draw = gray!30, >=latex

  }

  ]



  node[reserv=red] (HOT) at (0, 0){$T_textrm{tiny HOT}$};

  node[proc=yellow] (M) at (-2, -3) {$textrm{eff.} = eta_M$};

  node[proc=yellow] (L) at ( 2, -3) {$textrm{eff.} = eta_L$};

  node[reserv=blue] (COLD) at (0, -6){$T_textrm{tiny COLD}$};



  draw[arrow, ->] (HOT.south -| M) -- (M) node[left, midway, black]{$Q$};

  draw[arrow, <-] (HOT.south -| L) -- (L) node[right, midway, black]{$displaystyle{frac{eta_M}{eta_L}}Q$};

  draw[arrow, <-] (COLD.north -| M) -- (M) node[left, midway, black]{$(1 - eta_M)Q$};

  draw[arrow, ->] (COLD.north -| L) -- (L) node[right, midway, black]{$eta_M Qdisplaystyle{left(frac{1}{eta_L} - 1right)}$};

  draw[arrow, ->] (M) -- (L) node[below, midway]{$eta_M Q$};



  node[left = 0.1cm of M, black, align = center] {More\efficient};

  node[right = 0.1cm of L, black, align = center] {Less\efficient};

  node[above = 1cm] at ($(M)!0.5!(L)$){$eta_M geq eta_L$};



end{tikzpicture}

end{document}